Mayor Marion Barry withdrew yesterday his proposal to reduce trash collections to once a week in some parts of the city, bowing to community pressure and to strong opposition from labor unions and key members of the City Council.

"This is an idea whose time is kind of premature," Barry said. "It's not a matter of giving in . . . it's a matter of changing direction. That's what leadership is all about. I'm not afraid to withdraw an idea whose time is not yet right."

Standing in the hallway of the District Building beside one of the large, green 82-gallon rollaway trash carts that were to be an integral part of the pickup system, Barry said he still believed in the plan.

"I just support it totally," Barry said, thumping the top of the heavy plastic can with the palm of his hand. He said he would use one of the cans at home as an experiment.

Barry said he had erred in making the proposal without first getting a sense of how it would be received in the neighborhoods.

"Because of the early submission requirements of our budget process, we could not begin to sell this idea to the public in a logical and gradual manner," Barry said. "Trash [collection] is an emotional thing. You can't rationalize it. [People] have to see it, feel it and touch it."

Barry said yesterday that the proposal, whose abandonment marks one of the first major policy reversals of his 10-month-old administration, was not his own, but merely a staff recommendation. He said, however, that he would take responsibility for it.

"Being mayor, you take the lumps. You win some. You lose some. Sometimes it's a draw," Barry said.

A reporter asked which of those would best describe the outcome of this situation. "It's a draw," Barry responded, with a smile.

"That's a matter of interpretation," said Council Member Wilhelmina J. Rolark (D-Ward 8), one of the council members who most opposed the plan. j"I think the signals were clear," Rolark told Barry. "You're a very smart person. You read signals well."

Barry initially proposed reducing trash collections from twice to once a week in areas of the city east of the Anacostia River as part of his 1981 city budget. The mayor said the plan would eliminate 38 jobs from the city payroll and save nearly $700,000.

Council members, neighborhood leaders and union officials immediately criticized that plan. The east-of-the-river area already is among the poorest and most neglected in Washington, they said, and could least afford to serve as a laboratory for the experiment.

On Oct. 12, Barry modified the proposal. He said he would experiment with the new system in at least six sections of the city, basically all wards except those in the inner city.

Yesterday, however, Barry said that the experimentation would esentially be voluntary. More important, he formally restored to his budget proposal the job positions and funds that would have been eliminated if the east-of-the-river program had gone into effect.

"We'll put it to rest once and for all," Barry said. "In 1981, we'll continue the twice-a-week pickup in all wards."

The mayor said he would ask city officials -- including council members, Advisory Neighborhood Commissioners and others -- to join him in trying one of the larger cans as an experiment. Trial collections could begin early next year, according to officials of the D.C. Department of Environmental Services.

However, William Johnson, acting director of the department, said that with full funding in the 1981 budget for continued twice-weekly collections, the urgency behind the experimental pickups no longer would be present.

Barry's withdrawal did not satisfy leaders of District Council 20 of the American Federation of State, County and Municipal Employes, which represents the city's sanitation workers.

Shortly after he announced his abandonment of the plan, Barry met with union leaders in his refurbished conference room for a ceremonial signing of one-year extension of the present city contract with the union, including a pay increase that is expected to average 7 percent.

"This is supposed to be a happy occasion for us. But it's not," said Geraldine P. Boykin, executive director of the council.

"We still don't understand why it's necessary to bring those dumpsters in here for experimentation," Boykin said. She said the union also opposes Barry's continuing proposal to turn trash collection services in the inner city over to a private contractor next year. That plan and others still in the Barry budget would eliminate 99 jobs in the trash collection division of the department.

Once-a-week trash collection systems have been implemented with overwhelming acceptance in numerous cities throughout the country -- including Atlanta; Hampton, Va.; St. Petersburg, Fla.; and Shorewood, a suburb of Milwaukee.

In those cities, trash collection bills, workers' back injuries and rodent problems have been reduced. But it is still uncertain how well the plan could meet the test of trash collection in Washington, where there is more on-street parking, a major problem with rats, a larger population and many poor children who might play in the deceptively dangerous cans.

Barry said yesterday that if once-a-week collections were implemented citywide, the District's present $6 million annual trash disposal bill could be reduced to less than $2 million. "We hope to be successful in educating the public to the virtues of this plan over the next year," Barry said.

But those financial arguments failed to convince critics like Rolark, who along with other council members, joined Barry at the press conference yesterday.

"I want it to be very clear," Rolark said as she stood at Barry's side. "The only thing I like about this can is the color. I like green." She said she did not want any of the cans used in her ward, not even on a trial basis.

"Experiment someplace else," Rolark said.