The Metropolitan Washington Board of Trade announced yesterday that it was giving modest campaign contributions to three candidates running for an at-large City Council seat in next Thuesday's special election.

Refusing to make an endorsement in the race, the board's political action committee decided instead to give $300 each to the campaigns of lawyer John Ray, planner Hector Rodriguez and Warren A. Hemphill Sr., a city parole officer.

The decision to back Ray, one of the two front-running candidates, and two long-shot contenders was, according to sources close to the board, a result of some hidden support among board members for former council member Douglas E. Moore, who has been one of the harshest public critics of the board in the past, and is now trying for a political comeback.

"They couldn't endorse Doug because too many other members of the board can't swallow him because of his campaign last time," one source said. "But on the other hand, they would not oppose him . . . I think that helps Doug."

Many had expected the endorsement to go to Ray, who has the active support of Mayor Marion Barry. Ray has collected far more money from city businessmen than any other candidate and, unlike Moore, has not been publicly hostile toward the board.

Ray, however, supports a proposal for a referendum on the proposed $99 million downtown convention center, a project that businessmen are eager to see go ahead.

In addition, one member of the 10-person committee said, privately, Ray was "just not that impressive. None of them were."

Ray said he did not expect to receive the endorsement, and felt the decision not to formally support him would help to counter accusations that he is controlled by the city's business community.

"Everyone's been saying that I'm the business community's candidate, but they [businessmen] obviously don't like the way I voted on the convention center," Ray said yesterday. "People tend to support you if you're 100 percent with them. The Board of Trade is all tied up in the convention center."

During the past several years, Moore has been a strongly outspoken critic of the board. Its alleged influence on the council was the subject of a paperback book he wrote during his campaign for council chairman last year. The book was entitled "The Buying and Selling of the D.C. City Council."

His brand of shoot-from-the-hip politics was soundly rejected last year and Moore is now trying to make a political comeback as a new image candidate with a long-overlooked record of support for economic development in the city.

Sources close to the board said that some members of the political action committee support Moore because of his opposition while on the council to increases in the city's parking tax. Since coming on the council in January as an interim member, Ray has proposed doubling tax from 12 percent to 25 percent.

"It's the same old kind of mealy-mouthed thing the business community has done before," one board member complained privately. "They just go and support everyone. They're afraid if they don't support someone and he gets elected, they wouldn't be able to talk to him."

In the Ward 4 council race, the board endorsed Charlene Drew Jarvis and pledged $400-the maximum amount allowed-to her campaign.

The other candidate in the Ward 4 election are Mary G. Prahinski, Malcom Diggs, Ernest Bowman, Robert V. Brown, Vickie Street, Richard Clark, Goldie Cornelius Johnson, Andrew W. Coleman, Dorothy Maultsby, Gregory A Rowe, Nathaniel (Nate) Sims, Norman C. Neverson, Barry Campbell and William Revely.

In addition to Moore, Ray, Rodriguez and Hemphill, the candidates in the at-large contest are Frannie Goldman, H. Chris Brown, Jackson R. Champion, Stuart D. Rosenblatt, David G. Harris, Lin Convingon and Richard Blanks Sr.