A 26-year-old bartender who claimed he had a homosexual affair with Rep. Robert E. Bauman was charged in federal court here today with attempting to extort $3,000 from the congressman by threatening to disclose the relationship.

James E. Regina of Fishing Creek, Md., was arrested in Annapolis by FBI agents who learned about the threat from Bauman's lawyer last month.

The plan that led to the arrest was set in motion last Friday, the same day the Republican congressman appeared in court on the charge of soliciting a 16-year-old boy.

Regina was charged with making a threat through the U.S. mails and is being held on $50,000 bond.

According to law enforcement sources, Regina and Bauman have had a longtime homosexual relationship. Until June, Regina was employed as a bartender at the Cafe Naples, a Washington gay bar.

Regina was brought before a federal magistrate here at the same time Bauman was telling a press conference in Easton that he had "homosexual tendencies." Bauman said he had initiated the investigation that led to the arrest but emphatically denied that he had been blackmailed.

"I was not blackmailed," Bauman said. "I will not be blackmailed."

Asked if he knew the arrested man (Regina), Bauman said, "I do not recognize the person."

The FBI was brought into the investigation on Sept. 23 after the U.S. attorney's office was notified that Bauman's office had received a phone call from Regina, according to the affidavit. Regina, according to the affidavit. Regina allegedly told the congressman's staff that he had information about a grand jury investigation involving Bauman and wanted to talk to Bauman personally.

After Regina had called Bauman repeatedly, Bauman finally talked to him and Regina said he wanted $2,000 to "get out of the country, perhaps go to Hawaii," according to the affidavit.

By that time Bauman had received a letter from Regina, postmarked Sept. 30 in Fishing Creek, a small town on the Eastern Shore, containing an account of their alleged homosexual relation ship and a threat. Regina, according to the affidavit, threatened to "comfront" Bauman's family with the information and send a copy of the letter to Bauman's staff, "letting them know who I am and what we did." He also threatened to take the story to the press.

The letter demanded that $2,000 in $100 bills be sent to Regina in a brown envelope.

Last Friday, after receiving this information, an FBI agent, with Bauman's permission, phoned Regina at the home of his parents in Fishing Creek and introduced himself as a Bauman aide.

In recorded conversations with special agent David Loesch, Regina requested $3,000, but stated that he would be willing to take $2,000, according to the affidavit. In return, Regina offered to testify that he never had any sexual relationship with Bauman and the FBI was trying to set Bauman up, the affidavit stated.

Regina was arrested at 1 p.m. today in Annapolis by FBI agents.

He was described by law enforcement sources as a street hustler and a drug user. A court officer who interviewed Regina said he ws addicted to heroin, but had not used the drug for the last month.

Other law enforcement sources said that Bauman had met Regina on the Eastern Shore when Regina was a teen-ager, and that they had been "lovers on and off for years."

Regina had worked at the Cafe Naples on New York Avenue NW, in the heart of Washington's tenderloin district where homosexuals cruise the streets looking for young male hustlers. Regina, however, has been unemployed since early this summer and has been living with his mother and stepfather in the small Dorchester County town of Fishing Creek, on the Chesapeake Bay.

According to law enforcement sources, Bauman had once helped Regina's family by obtaining an early discharge from the Navy for Regina's brother, after the mother had requested Bauman's assistance.

For a time, federal law enforcement officials were looking into an allegation that Bauman had obtained the release in response to a blackmail threat to expose him as a homosexual. But they concluded that the evidence did not substantiate that allegation. Law enforcement officials could not show that Bauman, in obtaining the early release, had done anything other than provide a normal constituent service.