More than 40 D.C. city officials businessmen, labor and community did extravanganza at the District Building yesterday in an District Building yesterday in an eleventh hour show of "broad-based" support for the city's proposed $110 million downtown convention center, which is currently in jeopardy on Capitol Hill.

Large site diagrams stood propped-up on easels, a model of the proposed convention center complex hung from a lectern and the assembled spokes-persons filled the entire well below the City Council dias.

One by one, and sometimes in groups, Mayor Waltor E. Washington introduced members of the entourage, an each in turn told reporters that he was solidly behind the project.

Labor leaders talked of more jobs - the project is supposed to bring 4,000 of them - and businessmen talked of more taxes going into the city's coffers. They all ruled out any possible compromise on either the financing plan for the project or delaying it for another year.

The first $27 million to finance start-up costs for the convention center project is included in the city's 1978 budget. The House approved the project when it passed its version of the city budget, but the Senate, by a lopsded vote of 65 to 25, cut the center from the budget.

"The basic problem we have before us is to assert that we reaffirm our position," Mayor Washington said. If the project, which has the the overwhelming support of the city's elected leadership, is not approved by Congress, the mayor asserted, "the seeds of home rule" sown "over the past 20 years" are "going to erode before our very eyes."

Yesterday marked the second time in less than three weeks that city leaders, led by the mayor, had called reporters together to equate congresssional approval of the project with the integrity of the city's home-rule government, which has been in place since 1975.

After two meetings, a Senate-House conference committee that is supposed to resolve the convention center issue and 40 other disputed items in the two different versions of the budget bill reached an impasse on Monday. The conference committee has since adjourned without setting a future meeting.

Both sides are believed to be waiting for the other to take the first step towards a compromise, but so far, according to congressional sources, neither has done that.

The principal opponent of the convention center project is Sen. Patrick J. Leahy (D-Vt.), chairman of the Senate District Appropriations Subcommittee. Leahy believes the project should be supported by more private funds, is too costly may result in a need for more federal funds for the city and lacks full community support.

Sources on Capitol Hill said that yesterday's affair at the District Building was aimed at bolstering the leverage of Rep. William R. Natcher (D-Ky.), chairman of the House District Appropriations Subcommittee, on whom the city's convention center supporters are counting to pull the project through.

The fiscal year funded by the 1978 budget began Oct. 1, and the city is spending money only under the authorization of a 30-day special resolution. If a compromise budget bill is not hammered out and approved before the end of the month, the city's authority to write checks will expire, unless another continuing resolution is passed.

Yesterday's meeting at the District Building was a light-hearted and rousing session. After weekly newpaper publisher Calvin W. Rolark got an especially loud round of applause for his support of the project, the mayor called on a representive of the Committee of 100 Ministers by saying, "We've got the spirit of it now, Reverend, go ahead and send a message to the Senate."

Among the more well-known groups represented at yesterday's news conference in addition to the Ministers committee, were the Metropolitan Washington Board of Trade, the D.C. Chamber of Commerce, the Chinese Benevolent Association, VOICE, Greater Washington Area Senior Citizens, the National Press Club and several labor unions, Del. Walter E. Fauntroy (D-D.C.) and City Council Chairman Sterling Tucker also attended.