A confidential ethics investigation of prominent Washington lawyer Thomas G. (Tommy the Cork) Corcoran for reported lobbying of two Supreme Court justices has ended without a recommendation for disciplinary action.

The investigation, made by the Board of Professional Responsibility of the District of Columbia Bar, is "over and done with," a source told a reporter.

Few details were available. Board officials, in any case involving allegations of possibly unethical conduct by a lawyer, are forbidden to say if they have heard witnesses, dismissed the allegations or informally admonished the attorney.

The lobbying episode was reported by Bob Woodward and Scott Armstrong of The Washington Post in their 1979 book "The Brethren," an account of the inside workings of the Supreme Court. They said it occurred in 1969 and involved separate visits by Corcoran to Justices William J. Brennan Jr. and Hugo L. Black, who since has died. The only remaining eyewitnesses thus are Corcoran and Brennan.

Corcoran is believed to have provided board investigators with his account of the episode. The rules of the District of Columbia Bar, of which he is a member, require members to cooperate in investigations. He refused to comment, choosing not to respond to a reporter's written invitation to give his side and to disclose what the board had done.

Brennan also is believed to have provided his recollections of the episode, although he, too, refused to comment.

The investigation was requested by Adm. H. G. Rickover last December after he learned of the reported lobbying from an excerpt of "the Brethren" in the Post.

At the time, American Bar Association President Leonard Janofsky said that the book's account of the lobbying, if true, struck him personally as "a very, very serious violation" of the ABA's Code of Professional Responsibility.

As related in "The Brethren," Corcoran went to see Black, an old friend, and "shocked" him by complaining that an antitrust ruling involving the El Paso Natural Gas Co., the world's largest gas pipeline venture, was "a great injustice."

The ruling required El Paso to divest its holdings in the West, and it had filed a petition -- pending at the time of Corcoran's visit -- for a rehearing. Corcoran's law firm had been retained by Colorado Interstate Gas Corp., which also had fought the ruling, but his name was not on the rehearing petition or on other briefs and papers.

"Black cut his old friend off quickly," Woodward and Armstrong wrote. "No. He shooed Corcoran out of his office." In 32 years on the court, they said, "Black had never had the arm put on him in such an overt way in his own chambers."

The authors said that Corcoran next called on Brennan. Also caught unaware, "Brennan stood," they wrote. "He said that he, of course, could not and would not ever discuss a pending case, and showed Corcoran to the door. He immediately went to tell his clerks. Something awful just happened, he said."

The court almost never grants petitions for a rehearing, and it didn't grant El Paso's.

The reported lobbying appeared to have violated the Supreme Court's own rules, under which a lawyer who is "guilty of conduct unbecoming a member of the bar of this court . . . will be forthwith suspended from practice before this court."

Neither the book nor any subsequent development gives any hint that the justices ever have considered the possibility of applying the rules to Corcoran, who has been a member of the Supreme Court Bar since 1936.

The court's "neglect of ethical breaches by members of its own bar" troubled Bruce E. Fein, a member of that bar who compiles an annual summary of the court's decisions published by the American Enterprise Institute, and who is in the Justice Department's appellate section.

Writing last March in The Legal Times of Washington, Fein said the neglect mocks the "moral tutelage from the Supreme Court."

Fein recalled that Chief Justice Warren E. Burger, in his annual talk at the mid-year meeting of the ABA in February, "exhorted legal instructors to inculcate ethical standards and sensitivity in their students.

"The chief justice also implored the bar to greater discipline of members who flouted standards of professional conduct, declaring the commitment to ethical standards is measured by how vigilantly they are enforced," Fein wrote.