One of the California Supreme Court's most conservative justices told an investigating commission today that he had no reason to believe that Chief Justice Rose E. Bird or any other justice had delayed key court decisions for political reasons.

State Supreme Court Justice Frank R. Richardson, who sharply differs with the liberal Bird on most philosophical issues, said he knew of no evidence to suggest that either the chief justice or Justice Matthew O. Tobriner had stalled a decision striking down a state law the provides mandatory prison sentences for persons who use a gun in the commission of a robbery or other serious crime.

The court took 10 1/2 months, two to four months longer than ususal, to decide what Richardson termed a relatively simple case. Critics have charged that Tobriner held up the majority opinion long after the court had reached a decision, until Bird had been confirmed by California voters last November.

Richardson, a 1974 Ronald Reagan appointee, dissented from that decision.Last week he became part of a new court majority when a swing justice switched his vote and enabled the conservatives to issue a 4-to-3 decision upholding the mandatory prison sentence.

But Richardson's testimony today was helpful to Tobriner and Bird.

"I didn't fell then and I don't feel now that anybody was trying to hold the case up," he said.

Richardson gave similar answers when asked about the reasons for delay in decisions on three other controversial cases, one of which was before the court for 14 months.

Another witness before the commission today, Raymond Lee, chief deputy clerk for the court, also denied knowledge of any delays in the four cases.

The precedent-setting investigation by the California Commission on Judicial Performance also became an inquiry today into whether justices had "leaked" information to the press about pending cases.

Pointing to huge mock-ups of articles about the court that appeared in the Los Angeles Times, the Los Angeles Daily Journal and The Washington Post, commission special counsel Seth M. Hufstedler repeatedly asked Richardson whether he or his staff had been the source of articles critical of the court.

Richardson denied being the source of the information and said he disapproved of the leaks. He also recounted how Tobriner had called the justices together after one such article appeared in the Los Angeles Times, called the leaks "deplorable" and urged the justices to question their staff about them.

The article, published on election day, quoted court sources as saying that the mandatory prison sentencing case, known as People v. Tanner, had been decided, but that the opinion had been held up until after the election.

Hufstedler said he intended to question each supreme court justice about "leaks" to the press. He cited a judicial canon of ethics that prohibits justices from talking about a case before it is decided and said the commission wants to determine if any justice acted improperly by talking to reporters.

Because any justice who has done so could be reprimanded and any staff member could be fired, one probable effect of the investigation will be creation of greater barriers of secrecy around a court whose deep personal and ideological divisions have now become a matter of public record.

Information provided Monday by Hufstedler showed that Justices William P. Clark had exchanged memos with Bird and Tobriner in which each side accused the other of giving false information and acting in bad faith.

There was a reference to one of the U.S. Supreme Court's most famous decisions when the commission opened its meeting today by rejecting the claim of Justice Frank C. Newman that the proceedings violated a judicial privilege protecting the confidentiality of communication between justices.

Hufstedler cited the ruling of the U.S. high court striking down former president Richard M. Nixon's claim of "executive privilege" in the Watergate tape recordings case. Hufstedler said "full disclosure" was needed to allow the commission to carry out its duties. The commission met privately and then agreed with him.