A public inquiry designed to restore confidence in California's troubled Supreme Court has been forced into a secret session that seems likely to damage its reputation as the nation's most innovative judicial body.

After more than a month of public hearings into charges of impropriety by the justices, the court's inability to rule quickly on a constitutional challenge to the inquiry forced the state Commission on Judicial Performance to move its proceedings behind a closed door and a crudely lettered "Do Not Distrub" sign.

The action has caused dismay in the state's legal profession, many of whose prominent members had expressed shock at the damage they felt the hearings were doing to the court.

"They've managed to embrace the worst of both evils in the situation," said Edward Lascher, chairman of the state commission that reviews judicial appointments. "There's been a big public show, but with no conclusion and a veil of secrecy thrown over it at the last minute. What's left of the prestige of the court is going to suffer even more."

The commission originally opened the investigation to the public in an effort to restore confidence in the embattled court and avoid any appearance of a whitewash. The problem was compounded by the fact that four of the commission's eight members were appointed by the Supreme Court.

But now, in the wake of a lower court ruling that the public nature of the investigation violates the state constitution, there is doubt that the commission will even be able ti issue a public statement about its findings.

The commission was investigating allegations, first reported in an election-day 1978 story in the Los Angeles Times, that senior Justice Mathew Tobriner had delayed release of a politically explosive legal decision to help Chief Justice Rose Elizabeth Bird win confirmation by the voters.

In the course of its hearings into this and other charges, the commission exposed the deep and virulent views on the bench in which Bird, a former member of Gov. Edmund G. Brown Jr.'s cabinet, and Justice William Clark, onetime chief of staff to Brown's predecessor, Ronald Reagan, were the principal adversaries.

In testimony before the commission, Bird charged that Clark had sought to embarrass her on the court and allowed "politicial motivation" to cloud his actions as a justice. Clark denied this, and portrayed Bird as a suspicious, sometimes vindictive justice who snubbed him and feared that other justice and court aides were conspiring against her.

Clark also alleged that the court had delayed the filing of several controversial cases, and that Bird and her attorneys had "impugned" hsi character. Bird's attorneys responded that Clark's comments had "slandered" the chief justice, and claimed his testimony would be "impeached."

Central to any determination of the facts is the testimony of Justice Stanley Mosk, who reportedly warned Tobriner last fall he would have to "pay the consequences" for the delays by the court. But Mosk won a lower court ruling last week blocking his testimony on grounds the public hearings were unconstitutional. His statements on the dispute will now be heard in private.

What has been exposed in the case is a series of intense, highly personal and seemingly trivial feuds among various justices that continue to plague the court.

"The impact of the hearing has been considerable in reducing the esteem in which the court is held," said Lascher. "And I don't think that's because of any determination as to whether those cases were held up or not. What's had impact is the bickering and pettiness of the justices, and their seeming inability to perform their jobs. The naked antagonisms between some of them and the general lack of collegiality has been frightening."

The result, many legal observers believe, will be serious erosion of the court's once unchallenged power and influence.

"I'm afraid there are some very injurious implications in all this," said Preble Stolz, a law professor at the University of California. "Beyond the decline in public respect, I think there will be an increasing inclination on the part of other government institutions to second-guess the court and place more restrictions on its discretionary powers."

Stolz added that it will be very difficult for the court to continue its tradition of "judicial activism" that has made it a frequent pioneer over the last generation in civil liberties and civil rights decisions.

The court has relied on its reputation as an impartial and impassioned body removed from the tugs and pressures of California's often dissonant politics. But now, according to Seth Hufstedler, the special counsel who conducted the commission's investigation, that reputation is shattered "and the natural consequence is a strong adverse reaction to the court."

"The Supreme Court," he added, "will never be the same again."