By DAVID FIRESTONE with JOE SEXTON

Desmond Robinson went to extraordinary lengths to avoid looking like a police officer. He shaved his head but not his beard. He wore earrings to work, along with shorts and sandals. He became so good at dissolving himself into the fluid masses on the subways that his colleagues bestowed on him the ultimate nickname for an undercover officer: The Phantom.

He was the just the kind of adversary most dreaded by the roving bands of pickpockets who work the trains and spend more time looking for the police than they do hustling for the easy wallet. Most of them never get arrested, having mastered the art of spotting an officer's nervous glance through his disguise. But they rarely spotted Officer Robinson. "If you were a perp, he could be on you out of nowhere," said Sgt. Michael Conway, his former supervisor in the transit police.

Peter Del-Debbio did not wear a uniform to work, either, but came from a different corner of the city's sprawling law-enforcement community. A straight-arrow squad leader in the military reserves once a month, he spent his workdays in an elite unit of the police department's Organized Crime Control Bureau, working with the gadgets and tools of reconnaissance. Though a plainclothesman, he never had occasion to wear an earring to work.

He is white -- half Italian, half Hispanic -- and Officer Robinson is black.

The two men might never have met, had it not been for the kind of misunderstanding so possible and so deadly that the thought of it chills the blood of every police officer, in or out of uniform. Sometimes it nearly happens, but is averted at the last moment by a shout or a signal or an instant of recognition. Last Monday night, there were no such fortunate moments.

In the gloomy commotion of the 53d Street IND subway station, Officer Del-Debbio shot Officer Robinson four times, having been fooled into believing that the man in the brilliant disguise, who happened to be holding a gun, was a criminal. Two of the wounds were in the back, and witnesses said Officer Del-Debbio had continued to fire as his colleague fell to the ground or after he had fallen.

Stemming from familiar circumstances -- two youths carrying concealed weapons from Manhattan to Queens -- the incident became one of those crushing but perfect illustrations of how a police officer's life is divided into a series of split seconds. In a job where a decision must come faster than thought itself, the instinctual judgments about race and crime built into an urban culture are often more important than all the sensitivity training a police department can offer.

No one was killed in the incident, but Officer Robinson was seriously wounded. He is in stable condition at Bellevue Hospital Center with wounds to the heart and liver, on his way to recovery. Officer Del-Debbio, who was shot in the arm by another officer on the platform, was released from the hospital on Thursday after a distraught and apologetic bedside visit to Officer Robinson.

"He can't believe that's his face in the newspaper," said Detective Sergio Rivera, a good friend of Officer Del-Debbio's in the public morals unit, where he was previously assigned. "Of all the nightmares a cop can have, this is the worst. I told him I was praying for him, and he said to pray for the other guy."

Officer Robinson Accepting Danger, Handling Fear

There is more to being a daredevil than riding a motorcycle, learning kung fu and training for a helicopter pilot's license, although Desmond Robinson did all of that. Even more risky in the circumscribed culture of the police was listening to -- and liking -- the music of the rapper Ice-T, who ignited a firestorm a few years ago with his song "Cop Killer." Where others heard a furious diatribe urging the execution of cops, Officer Robinson heard a song about bad cops, who murdered and broke the law.

"He'd say it was about killing criminals," said Lieut. Bobby Wheeler, who trained Officer Robinson in the Police Academy and later served as his superior officer with the transit police. "He understood the message. He'd raise eyebrows, but Des stuck to his guns."

Desmond Robinson never did care much about conformity, at least not until he had to learn to blend into the tide of subway passengers. Growing up in an apartment in the West Brighton section of Staten Island, the youth known as Skip did not bother hanging out with the other teen-agers, putting up with their taunts when he said he wanted to be a policeman.

"We didn't believe him," said Robbie Edgeworth, who lived down the hall from him. "But he did it."

'Down in the Hole'

First he put in a stint in the Marine Corps, stationed in San Diego, then he took the police exam, hoping to be assigned to the New York Police Department. Instead, he drew the transit police, and grew to love it.

"He was a tunnel rat," said Detective Billy Nolan, a longtime friend who was also in the 1986 class of recruits. "He said he loved it down in the hole. He said the steel dust made him strong."

After four years in uniform, Officer Robinson moved in May 1990 to the plainclothes anti-crime unit of District 4. The unit handled a variety of duties, from summons sweeps to the rousting of panhandlers to elaborate robbery stakeouts and setups. In tandem with his partner, David Thompson, he proved remarkably adept at the intricate, subtly clandestine work of the plainclothesman on the trains. The two became good enough to be known to fellow officers as the Dynamic Duo and were praised by their superiors for the quality of their arrests.

"The criminals in the subways are always looking for cops -- it's absolutely essential for them to be able to make cops," said Deputy Inspector Joseph Madden, who served as Desmond Robinson's commanding officer in District 4 for a year. "It's tough work to blend in, to do your job at the same moment you are doing your best to act completely uninterested. Des and Dave were good. Better than most. It's saying a lot."

'War Zones'

As friends and members of the loose fraternity of other black undercover and plainclothes officers, the two knew full well their vulnerability amid officers who did not know them and might assume that they were criminals. Some stations were considered "war zones" for black undercover officers, who knew if they were seen with a weapon drawn, they could "get done," to use their expression.

"You can't keep sweeping these things under the carpet," said Officer Randolph Blenman, a black plainclothes officer in the same unit. "If you are an African-American officer working plainclothes, there is a special risk. When does the education that not every man with dark skin and a pistol is a target begin? When one of us is dead."

The department requires undercover officers to wear a wristband or headband corresponding to the colors of the day, which all officers are supposed to check daily to identify those working undercover. But Officers Robinson and Thompson took added precautions, letting uniformed officers get to a scene first, if possible, and describing themselves in detail on the radio when responding to a call with guns out. Officer Blenman said Officer Robinson enjoyed the work, understanding the danger but handling the fear.

Difficult Assignment

Among the most difficult arrests to make are those of pickpockets, who are often repeat offenders, and who never forget the face of an officer who has arrested them. They work in groups of as many as five operatives, playing draining games with their undercover opponents. Pickpockets board trains, wait until the exquisitely perfect last second and then step off. If anybody else does it, he's a cop.

Lieut. Charles Irving of the elite citywide pickpocket unit said the work humiliates and defeats roughly 40 percent of the officers who are chosen to give it a try. Officers Robinson and Thompson had interviewed and tested to join the pickpocket unit last year. They were not selected, but they scored highly enough that, when the unit required some temporary additions three weeks ago, the partners were called.

Last Monday, Officer Robinson was there at the Citywide Task Force offices for 3 P.M. roll call, wearing his bulletproof vest. He made no arrests that afternoon, and was last seen by a superior when he met with his sergeant at the Grand Central station between 4 and 5. Three hours later, he was near the tollbooth of the 53d Street IND station. And despite regulations, he was no longer wearing his bulletproof vest.

Officer Del-Debbio Proud to Be Part Of an Elite Unit

Peter Del-Debbio already knew the menace the subway system could contain. In August 1990, he was riding the N train home with his future wife when three young men boarded the train at the East 60th Street station and attacked him. While one man held a knife to his throat, the others searched him and found his service revolver and a police union calendar. Realizing they had a police officer at bay, one of the men bit him in the chest and arms while another used the revolver to bruise him over the eye.

Then, as two of the men held down Officer Del-Debbio, the man with the knife sliced off the tip of the officer's trigger finger, saying, "He won't be a cop for long." They fled at the next station.

The assailant's prediction proved incorrect. Though Officer Del-Debbio worried for months about his disability, it did not stop him from returning to the 103d Precinct in Jamaica, Queens, and the job that he had wanted since childhood. Friends said the only damage from the incident they could detect was his maimed finger.

"You would have thought it would bother him, but I never heard him bring it up," said Investigator Leonard Devlin, his partner and close friend in the public morals division. "He bounced right back and rode the subway all the time. It never interfered with his life."

Considered Priesthood

Officer Del-Debbio was born in New York City in October 1962, the son of a dentist in Astoria, Queens, who moved the family upstate to the Lake George area eight years later. His mother, Dahlia Del-Debbio, wanted him to be a priest, and he briefly considered the possibility after years as an altar boy and a few months as a novice with an order of monks. But he preferred the thought of police work.

After graduating from high school in 1980, he became a military policeman in the army, and stayed in uniform from then on. Even after he moved from being a staff sergeant in the military to the city police department in 1988, he remained in the reserves, and is still a squad leader with an M.P. company based in Uniondale, L.I.

Officer Del-Debbio spent four years in the 103d Precinct, receiving several commendations from residents and few complaints, according to police officials. But one Queens Village resident says he remembers an incident of racial bias in 1987. The man, Kevin Mallett, 32, a former van driver, says he was in a holding cell at the station house on a traffic violation when Officer Del-Debbio approached him, burped in his face, and said, "You don't matter anyway, you're nothing but a nigger."

Mr. Mallett did not file a complaint at the time, and has no records to verify his story. He says he saw Officer Del-Debbio's picture in the newspaper last week and contacted C. Vernon Mason, the civil rights lawyer.

Police records show that Mr. Mallett has been arrested three times since 1985 for criminal impersonation, possession of marijuana and resisting arrest. A police spokesman said there was nothing in Officer Del-Debbio's record about the incident.

'Mature Professional'

The officer's colleagues and relatives say he has never shown any sign of racial animus. "That's totally off line, completely wrong," said Lieut. Timothy Collins, his supervisor in the public morals unit. "He was a dedicated, mature professional. I wish we had more guys like him."

Last year, Officer Del-Debbio moved to the Manhattan South district of the public morals division, working in a small unit called the Late Tour Conditions Module. Beginning their shifts at midnight, members of the unit raided illegal social clubs, arrested street prostitutes, and closed down brothels and gambling dens. Members of the unit said they frequently had to draw their guns on the job, but said Officer Del-Debbio was never involved in a shooting incident.

His partner, Officer Devlin, said the officer was well liked around the unit, buying coffee for his colleagues and working long hours. A hunter and a hiker who loved the Adirondacks, Officer Del-Debbio gave up several days of vacation time to help in the unsuccessful search for the body of Sara Anne Wood, who disappeared in that region last year, Officer Devlin said.

'Proud to Be Here'

In March, after the hours of the late tour unit began to take a toll on his marriage to Denise Del-Debbio, an accountant, Officer Del-Debbio received a transfer to the technical services unit of the Organized Crime Control Bureau, based at police headquarters. The small unit, which is in charge of the bureau's surveillance equipment, from videotapes to undercover bugs, is considered elite.

"You are proud to be here, and he was," said his colleague in the unit, Officer Bryan O'Byrne.

On Monday, Officer Del-Debbio was wiring together a rack of video recorders when the other unit members left for the day at 6 P.M. Officer O'Byrne urged him to come, too, but he insisted on staying until he was finished. At 6:45 P.M., he left the unit and boarded an uptown subway train, transferring at 53d Street for the E train that, on any other night, would take him to Queens and the bus home to Franklin Square, L.I.

Monday Night Seeing a Gun, An Officer Fires

At 7 P.M., Desmond Robinson was standing with David Thompson and four uniformed transit police officers near the tollbooth of the 53d Street IND station, a long escalator ride up from the train platform. In the various accounts of what began to happen next, everyone agrees that two exiting subway passengers came up to the officers and told them they had just seen two teen-agers with guns down below.

All six officers began hurtling down the up escalator to the platform, where an E train to Queens was idling. When they reached the bottom, one officer saw Damal Parham, 16, drop a .22-caliber derringer on the platform, and arrested him. Two uniformed officers took Mr. Parham upstairs.

Police officials say that the other teen-ager, Shea Kisine Davis, 17, began to run down the platform when he saw his friend arrested, pulling a sawed-off shotgun from a slit in his pants where it had been concealed. In desperation, the youth tried to drop the shotgun in the space between the E train and the platform, but the gun hit the platform and fired loudly. Some of the pellets hit the legs of a bystander, Patricia Coples, who received minor injuries.

Grabbed the Shotgun

The shotgun landed outside the open door of the car where Peter Del-Debbio was standing in his usual plain clothes. He had transferred to the train and was heading home, having no idea that anything was happening on the platform until he heard the shotgun blast.

He quickly reached down and grabbed the shotgun and the first thing he saw was Desmond Robinson, in his usual disguise, moving down the platform with his gun drawn. Then Officer Del-Debbio pulled out his own .38-caliber service revolver.

There are several divergent accounts of what happened at the next, climactic instant. Friends of Officer Thompson say he saw Officer Del-Debbio, whom he did not know, standing with his gun in the car, and he yelled to his partner, "Des, he's got a gun." When Officer Robinson turned to his right, toward the train, Officer Del-Debbio shot him, and he fell to the floor. Officer Thompson said Officer Del-Debbio continued to fire while his partner lay prostrate, said the friends, who spoke on condition of anonymity.

Officer Thompson said he saw Officer Del-Debbio "pump three bullets into his partner while he was face down from a distance of about one foot," said a friend of Officer Thompson. "He looked into the officer's eyes and saw hate."

Remembering the Shots

This account is supported by Dennis Kearns, a New Jersey commuter who told police he saw Officer Del-Debbio kneel over Officer Robinson and fire his gun three times at point-blank range into the man's back.

Officer Robinson remembers being shot twice in the front before falling, then being shot twice in the back as he lay face down, said Brian O'Dwyer, a lawyer hired by the wounded man's family, who revealed the officer's first memory of the incident on Friday. Mr. O'Dwyer said Officer Robinson remembered a substantial interval before the final two shots were fired.

"He said he could not understand why he was shot on the ground -- that an officer should stop shooting," Mr. O'Dwyer said.

Police Commissioner William J. Bratton has said Officer Del-Debbio was not motivated by a racial hatred that caused him to fire at a prostrate man, a violation of police rules. He said other witnesses have said the first shots into Officer Robinson might have spun him around so that the subsequent shots entered his back.

Officer Del-Debbio, who was shot in the arm a few seconds later by another transit officer, had pulled out his badge, but did not shout, "Police! Don't move!," the standard departmental warning, police investigators said. Officer Robinson's badge was still in his pocket when he arrived at the hospital, and he was not wearing the colored band that could have identified him as an undercover officer. Perhaps it would have interfered with his perfect disguise.

Copyright 1994 The New York Times Company