The D.C. Zoning Commission voted tentatively last night to require developers to create housing along with the office buildings that they have geared up to build in a broad area of downtown between Pennsylvania Avenue and M Street NW.

The preliminary 3 to 2 vote, which followed months of often bitter debate, was the commission's biggest step yet toward creating a "living downtown" where more people live as well as work. If the body stands by its decision in a second vote that is expected in November, it also would pose some of the city's strongest demands yet on downtown developers.

The commission predicted that the proposed zoning changes would add 6,000 housing units in the East End, Chinatown and the area around Mount Vernon Square. The plan would allow developers to fulfill 30 percent of their housing obligations by subsidizing housing in other parts of the city, and those subsidies would be expected to generate another 4,000 housing units.

To make the housing requirements more affordable to developers, the commission approved zoning changes that appeared to increase slightly the amount of new development that can take place in affected areas of downtown.

The commission left some key details of the plan unresolved, opting to revisit those issues at a November hearing.

In a series of public hearings early this year, a coalition of urban planners and downtown activists argued that more housing would make downtown safer, livelier and economically stronger in the long run.

But representatives of the building industry said the housing requirements would impose an unmanageable burden on new development, curb the growth of the District's real estate tax base and consume development profits that could have been used to create more housing in other parts of the city. Developers also argued that they should be allowed to build offices downtown and provide housing in other neighborhoods.

The housing plan endorsed last night was not as stringent as some earlier versions that had been considered, but it was considerably more demanding than alternatives advanced by developers and Mayor Marion Barry's city planners.

"Finally, we've been moved toward taking our place with the great capitals of the world," said housing activist Terry Lynch, a leader of the coalition that prodded the zoning commission to require downtown housing.

"The big losers in all this are the outside monied interests," Lynch said, referring to developers.

Critics of downtown housing requirements had testified that the resulting housing would be priced for affluent professionals instead of poor families.

Commission members Lloyd Smith, head of a community development organization in Southeast, and Maybelle T. Bennett, who works for a think tank that studies poverty issues, voted against the plan.

Smith and Bennett urged the commission to allow developers to produce more of the housing outside the downtown area. Bennett repeatedly said the commission was losing sight of economic "realism."

During a four-hour meeting that continued late into the night, commission members said they were frustrated that they were called upon to craft a housing policy for downtown through zoning alone. Some members said that an effective housing policy would require other measures beyond the commission's authority, such as tax abatements for developers.

The commission was poised to make a decision in July but postponed a vote, partly to give a consultant time to study how the housing requirements might affect D.C. revenue. The consultant's report, which was completed last week, concluded that it is impossible to predict how the proposed zoning changes would affect tax revenue.

Despite the many elaborate written proposals and the testimony from 134 witnesses that it had considered since December, the commission ended up endorsing an improvised plan offered last night for the first time by zoning Chairman Tersh Boasberg. The highly technical plan left many developers, planners and others at the meeting in confusion.

"We are not sure what this is going to produce," Smith said at one point in the discussion.