Deatrice Brown and her 9-year-old daughter Jajuana were leaving the Simons Elementary School playground, headed home after school, when they saw the man.

He was on the neglected grounds of the vacant and vandalized Mott Elementary School next door. His trousers were down around his knees and he was masturbating.

"I pushed my baby behind me and ran back to the school," Brown said, recalling the incident two weeks ago. The man was standing beside Mott school, a two-story red brick building community residents say has become a heroin shooting gallery, the home for at least one vagrant and a magnet for other undesirables.

Used syringes are a common sight in the vacant school at 4th and W streets NW., and junkies congregate on its steps a few feet from the small children playing on the Simons playground.

Visitors to the building last week found several matchbooks and burned soda bottle caps which appeared to have been used to prepare drugs for injection.

Simons Principal LaVerne H. Cozzens speaks for many in the neighborhood when she says she is fed up with the Mott nuisance. They want the 71-year-old building occupied or demolished.

"If you are the owner of a home you wouldn't want that in your back yard and as the principal of this school I certainly don't want it in my back yard," she said.

Cozzens and many parents are afraid that a neighborhood child will be harmed by one of the men hanging around the vandalized school, which is across the street from the Kelly Miller and LeDroit public housing projects.

"It would be easy for someone to grab one of the little ones and take them to that building and do anything to them," said Deatrice Brown, PTA vice-president.

Leola Bynum, the mother of another 9-year-old at Simons, echoed her fear. "I'm afraid that one of the children will be raped or one will be killed" because the weeds growing around Mott school are taller than the children.

They also are afraid that an addict or vagrant will start a fire in the Mott building which could spread to Simons.

Maefield Joyner, president of the Simons PTA who lives across from the school, said at least two fires were started in the weeds in front of Mott this summer.

Principal Cozzens said she believes that people frequenting Mott were responsible for two burglaries at Simons this summer and in late September. She said intruders stole a tape recorder, a television set and food from the cafeteria, including 150 pounds of hamburger.

"If they need money to support a habit, where is the closest place to go?" she asked.

Police say that like any vacant building, the school has become "a haven" for derelicts and drug addicts. Citizen complaints about drug use have led to two arrests and frequent police surveillance of the school, said Fifth District Commander Carl Profater.

Meanwhile, District government and Howard University officials have been dickering over a lease for the building since it was closed three years ago when a new school replaced it. Howard University, a block away, wants to lease the school because the university is critically short of classroom space.

"We really want the building," said Dr. Caspa L. Harris, university treasurer. "It's ideal for our use."

But the university and the Department of General Services, landlord for the city, have been unable to come to terms. The university wanted to pay a nominal fee for a long-term lease because renovations will cost between $2 million and $5 million. The city has said Howard must either pay the market rent or settle for five years' use.

The school needs major renovations because vandals have made off with its copper pipes, stolen bathroom fixtures and water fountains, broken numerous windows, ripped blackboards from the walls and left excrement on floors.

Negotiations between the city and Howard were suspended between March 1978 and December 1979 when the school board reclaimed the building, telling the city government it had been mistakenly conveyed to the city government in October 1977.

When the city sent the university a lease in March which still included the five-year provision, Harris said, he put it aside temporarily out of frustration. "After almost two years and we still come up with five years, why hit your head against the wall," he said.

Last week the two compromised and seemed to have broken the impasse, at least orally, but the city still must have the building appraised, prepare a lease and negotiate its details with the university, arrangements which could take months.

But Cozzens and the parents want action now.

"I don't want to wait until a child gets hurt or a fire starts or somebody overdoses before something gets done," Cozzens said. "Inhabit the building or tear it down, because sitting there vacant isn't doing anybody any good."