WASHINGTON (AP) _ The Massachusetts Bar has opened preliminary disciplinary proceedings against Rep. Barney Frank, D-Mass., who recently admitted paying a male prostitute for sex, the Washington Times reports.

The proceedings were triggered when George Washington University professor John F. Banzhaf III last week filed a complaint with the state's Board of Overseers.

Assistant Board Counsel Terence Troyar told The Times in an interview from Boston on Friday, ''The board's proceedings are confidential, and I can neither confirm or deny that proceedings are under way against any individual.''

But Troyar confirmed that such proceedings are automatic once a complaint has been filed. Frank has 20 days to respond in writing, and Banzhaf may then submit a counter-response.

A bar inquiry could produce sanctions as serious as disbarment. Frank has never practiced law and is listed as an inactive lawyer by the board.

Such inquiries are normally kept confidential, but Banzhaf has asked Frank to agree to open them.

''He says the matter should be cleared up,'' Banzhaf said. ''Certainly, the public wants to know, and the best way is through a relatively neutral forum (the Board of Overseers), which has the expertise to resolve these kinds of issues.

Frank, who is gay, admitted last month that he paid prostitute Stephen Gobie for sexual services, then hired the man to be his personal aide. Frank said he knew Gobie was continuing to work as a prostitute, but denied knowledge that Gobie was running a prostitution service from the congressman's basement apartment on Capitol Hill. He said he fired Gobie in 1987 when he found out.

Frank also said he wrote several letters to Gobie's probation officer seeking to suspend the prostitute's probationary period, and that he used his congressional immunity to void Gobie's traffic tickets.

Frank himself has called for an investigation into the matter by the House ethics committee, saying he wants to clear the public record.