The purple and gold trucks of Ridgewell's Caterers were loaded and ready to go by Wednesday afternoon with hundreds of lavishly prepared dishes, including scallopine of fresh salmon and souffle of peaches topped with cream and raspberry sauce.

But the food, intended to help D.C. officials woo Democratic party officials here judging the city's bid for the party's 1984 national convention, never made it to the Washington Convention Center, where Mayor Marion Barry yesterday hosted a lunch for the site selection committee or to a dinner for committee officials at the Sewall-Belmont House on Capitol Hill.

The lunch and dinner went off without a hitch but also without Ridgewell's, which was booted off the job after a key city union official complained that Ridgewell's was a nonunion company.

A company with more solid union ties, B & B Caterers, was called in at the last minute by image-conscious convention center officials who along with other city officials have lobbied hard to pull off Washington's longshot bid for the national convention.

Ron Richardson, secretary-treasurer of Local 25 of the Hotel and Restaurant Employees union here, said convention center and Democratic officials were told Wednesday "we would be extremely upset if Ridgewell's did the thing."

"It doesn't make a hell of a lot of sense," Richardson said, for the city to try to curry favor with the national party, which is strongly dependent on labor for support, by hiring Ridgewell's. "They are an antiunion company and they also happen to be a Maryland company, not a D.C. company," Richardson said.

Bruce Ellis, coowner of Ridgewell's, denied that the company was antiunion. "We're just not a union shop," he said.

A spokesman for the Democratic National Committee confirmed yesterday that party officials urged convention center officials to switch to another company. "It's our policy to patronize union organizations," said Robert Neuman, director of communications for the national party. "We were a little surprised that officials of the convention center had not considered that."

A city official familiar with the situation, who asked not to be identified, said Ridgewell's and B & B are among several catering companies that have been used at the center, which opened in January, while the center waits for its kitchen to be completed.

The official said that the center, its private food concessionaire and the host committee coordinating the city's effort for the national convention may have to reimburse Ridgewell's for its expenses. In addition, Carl Longley, president of B & B, said he expects his bill to be about $45,000, a cost driven up by his last-minute preparations. A spokesman for Ridgewell's declined to say what Ridgewell's bill will be.

Ellis, Ridgewell's coowner, said the company carefully planned the events with convention center officials, right down to the color of the tablecloths and the type of china.