By JENNIFER STEINHAUER

Holding back tears, the parents of a 13-year-old boy killed last week by a housing police officer -- who mistook his toy gun for a real one and his game of cops and robbers for something more menacing -- appealed to toy stores yesterday to exchange toy guns for other playthings.

"Children cannot play games as we did when we were young," Angela Heyward, the mother of the boy, Nicholas Heyward Jr., said at a news conference at Intermediate School 293 in Brooklyn, where her son attended eighth grade.

A year after the owner of a Manhattan carpet store offered gift certificates for toys to anyone who would turn in real guns, educators and community leaders are joining the boy's family in appealing to children and toy stores to take part in a trade-in of toy guns, which they say can only lead to other accidental deaths.

"We are appealing to Toys 'R' Us to exchange guns for some other toy, " Mrs. Heyward said. "Society is different now. It's sad that they don't have a real childhood, but I lost a son."

Calls to Michael Goldstein, the chief executive officer of Toys 'R' Us in Paramus, N.J., were not returned yesterday. Managers at several local toy stores seemed to need time to mull over the toys -for- guns exchange idea, but Leonard Ungaro, the owner of Wonderland Toys on 11th Avenue in Brooklyn, said he would seriously consider such a program, if one were organized.

" Toy guns are not for everyone," Mr. Ungaro said. "If people feel that they need a program like that, I would agree to it."

The police say Nicholas Jr. was shot by a housing police officer, Brian George, who was responding to a call reporting that shots had been fired at 417 Baltic Avenue in the Gowanus Houses early on the evening of Sept. 27.

On the roof of 423 Baltic, Nicholas and a group of friends were busy with toy guns and a childhood standard -- cops and robbers -- when he and his 18-inch play weapon were spotted by the officer, who apparently shot him once in the chest. He died several hours later at St. Vincent's Medical Center.

The shooting outraged many residents of the Gowanus Houses -- who posted signs around the project that read things like "Whose 13-year-old is next for Robocop" -- and prompted religious and community leaders to appeal to parents to rid their homes of the toys.

A woman from Ghana, Naa Asie Ocansey, who said she has been traveling through the United States promoting nonviolence programs to young people, will offer teddy bears in exchange for toy guns through various schools throughout the city and with the assistance of the 76th Precinct, beginning with Nicholas's school next month.

Last year, Fernando Mateo startled the Police Department and the city with his successful campaign to exchange Toys 'R' Us gift certificates for weapons turned in to the 34th Precinct. He received hundreds of guns and extended the program by a month, and it caught on in other cities.

"I just ask that you find some way to stop making these guns, " the boy's father, Nicholas Heyward Sr., said yesterday, his voice shaking. "It's a shame that it takes the loss of my son to get this kind of attention."

He sat at a table littered with plastic guns, some of them bright orange and obviously phony, others eerie in their similarity to real assault weapons.

Students in green jackets handed out little green memory ribbons at the news conference and listened intently to the Rev. Herbert Daughtry, the pastor of the House of the Lord Pentecostal Church in Boerum Hill, Brooklyn. "It is important," Mr. Daughtry said, "that we take this tragedy and turn it into something positive."

Michael Shepherd, a 13-year-old friend of Nicholas Jr., said only: "I loved him so much. I can't believe he died for anything."

Copyright 1994 The New York Times Company