House Democratic leaders have decided to postpone action on a resolution to expel Rep. Mario Biaggi (D-N.Y.) until at least after his trial next month on racketeering and bribery charges involving the Wedtech Corp., leadership sources said yesterday.

But the sources said they will not wait until completion of his appeal of a September conviction of accepting an illegal gratuity and obstructing justice, because the appeals process will likely stretch beyond the November elections.

House ethics committee Chairman Julian C. Dixon (D-Calif.) acknowledged the delay in a statement yesterday, noting that Biaggi is involved in "other litigation" and "the committee believes the congressman should be given every opportunity to personally offer his views and argument in connection with the committee's recent action. Therefore, the committee intends to bring the matter before the House for consideration when an appropriate time can be established with Congressman Biaggi in order to allow for his participation in the floor proceedings."

The panel, formally known as the Committee on Standards of Official Conduct, voted Feb. 18 to recommend expulsion of the 10-term Bronx congressman and decorated police officer, who was convicted Sept. 22 of illegally accepting a paid Florida vacation from Meade Esposito, the former Brooklyn Democratic leader who was seeking government help for Coastal Dry Dock and Repair Corp. The corporation owed $280,000 in premiums to Esposito's insurance brokerage firm.

He was sentenced to 2 1/2 years in prison and fined $500,000.

If expelled, Biaggi, 70, would be only the second member of Congress ever ousted for official corruption. Rep. Michael (Ozzie) Myers (D-Pa.) was expelled in 1980 following a bribery conviction in the Abscam scandal. Three congressmen were expelled during the Civil War for treason.

There were indications earlier that the Democratic leadership, sensitive to any scandal in an election year, might move quickly. But pressure built to give Biaggi more time to prepare his case.

House Republican leader Robert H. Michel (R-Ill.) met this week with House Speaker Jim Wright (D-Tex.) to urge him to slow down. In a letter to Wright, Michel said he is concerned with "the manner in which we are apparently rushing to judgment against a colleague. . . . "

Michel said many House members had not read the ethics committee report, "yet there seems to be a fervor to bring our colleague to the floor for expulsion. Does one assume that if his appeal renders a reversal of his conviction that we then repeal his expulsion?"