Three men who posed as police officers and tried to extort $10,000 from a former Silver Spring man after accusing him of committing a homosexual act in a hotel restroom, were convicted by a federal jury yesterday of extortion and other criminal charges.

Assistant U.S. Attorney C. Madison Brewer said in U.S. District Court yesterday that two of the defendants face charges in Massachusetts in connection with a similar scheme, and that all three men are under unvestigation by a Florida grand jury, where they are alleged to have operated a similar extortion plan.

"These men are a bunch of bad characters," Judge Barrington D. Parker commented from the bench yesterday after the jury had delivered its verdict and left the courtroom. Parker released all three men on high money bonds, but made it clear that he expects to put them in jail when he sentences them on Feb. 13.

"I intend to have them stepped back," Parker said, using courthouse jargon for immediate incarceration after a courtroom proceeding.

The three men convicted are Loy Franklin Dove, 46, of Laurel; Thomas William Tavenner, 46, of Pepperell, Mass., and Francis Bernard Donahue, 56, of Jeffersonville, Ind. All three men face a maximum of 27 years in prison and substantial fines for their convictions of extortion and racketeering-related offenses and for impersonating police officers. The defendants said they would appeal the verdicts.

FBI agents and District police arrested the three men in Washington last June after the target of their scheme, a federal government employe, told law enforcement officials that he was being blackmailed.

The victim testified in court Monday that he had been on a lunchtime stroll along Connecticut Avenue and had stopped in the Mayflower Hotel to use the restroom where a man began to make lewd gestures. The victim acknowledged that body contact occurred, but prosecutor Brewer had emphasized earlier that no criminal act had occurred.

The victim testified that he panicked when the man suddenly displayed a silver badge and said to him, "That's all I need, you're under arrest."

The victim testified that he was then brought to the lobby of the nearby National Geographic Building, where he was questioned both by the person who approached him in the men's room and a second man.

To his relief, the victim told the jury, the two men eventually told him they would not bring any criminal charge against him. A few days later however, the victim received a telephone call and was later told that the "police officers" were in trouble because of the manner in which they had handled the case.

A third man, who described himself as a "lieutenant," offered to destroy a warrant for the victim's arrest in exchange for $10,000. According to evidence in the case, the "lieutenant" eventually agreed to take $2,800, which was all the victim had.

At that point, the FBI came into the case and tape recorded a telephone conversation, introduced in court, in which a rendezvous was set up at the Carter Barron amphitheater on upper 16th Street NW, where the three men were arrested.

The three are scheduled to stand trial in a second case in which they allegedly were paid $10,000 by another high-ranking government employe in exchange for their agreement to "dismiss" a charge against him for alleged homosexual activity in the Harrington Hotel in April 1979.