The senior justice of the California Supreme Court today accused another justice of improperly suggesting that a controversial case be decided by the court and the announcement suppressed until after last November's election.

The accusation came from the senior justice, Mathew O. Tobriner; who has been named in previous news accounts as the court member most responsible for the delay. But Tobriner said the suggestion was made not by him but by Justice William P. Clark, the conservative justice who has been most critical of the court's slowness in issuing the decision.

Tobriner said the idea, which he called "an extraordinary proposal and one that I thought was far out of line," was broached by Clark during a conference in Tobriner's office late in September or early in October of last year.

Clark, who was attending today's meeting of the California Commission on Judicial Performance, which is investigating the allegations, declined to comment. However, past statements by him indicate that he will dispute Tobriner's accusation when he testifies next week.

The case in question is People vs. Tanner, which challenged a California law imposing mandatory prison sentences on persons who use a gun during commission of a robbery or other serious crime.

In a 4-to-3 majority opinion written by Tobriner, the court in December invalidated this law after considering it for 10 1/2 months. Subsequently, the switch of one justice prompted the court to reverse itself and uphold the law in a 4-to-3 decision written by Clark.

Both Tobriner and Clark have political backgrounds. Tobriner, one of the court's most liberal justices, was a major figure in half a dozen Democratic political campaigns before he became a judge. Clark is a former executive secretary to ex-governor Ronald Reagan, who in 1974 appointed him to the state high court.

The Tobriner-Clark conversation last fall came against the backdrop of a bitterly fought election in which four members of the court faced a statewide confirmation vote.

Most of the controversy centered on the confirmation of Chief Justice Rose E. Bird, a former high official in Gov. Edmund G. (Jerry) Brown Jr's. administration.

One of the issues raised by those opposing Bird's confirmation was a rape case, known as Caudillo, in which the state supreme court decided that a particularly highly publicized rape did not constitute "great bodily harm." Bird said it was up to the legislature to write a new definition of "great bodily harm" if it wanted cases like Caudillo to be so considered.

When the case on mandatory prison sentences for criminals who use a gun came before the court, Bird wrote a separate opinion saying that the legislature had no power to prevent judges from granting probation. In a footnote to his dissent on this case, Clark contended that the chief justice was contradicting herself.

Subsequently, according to testimony, Bird called Clark's comment "politically motivated," and asked him to delete the reference.

Tobriner said Clark was upset by this charge, and said that, if the chief justice really thought that what he was doing was politically motivated, the case could be held up until after the election. This suggestion, said Tobriner, "horrified" him, and he told Clark that he thought he should delete the footnote instead.

Subsequently, Clark elevated the footnote to the body of his dissenting opinion.

Today's testimony in effect put the accused in the position of accuser, and took the focus away from the persistent efforts of special counsel Seth M. Hufstedler, who is trying to determine the reasons Tobriner held the opinion on his desk for 3 1/2 weeks in late August and September without taking any action on it.

Tobriner said his heavy workload and a statement made to him by Bird that another justice, Wiley Manuel, wanted to "do something" with the opinion prevented him from getting to it.

What Manuel subsequently did was write a separate dissent, an action that ensured that the final decision would not be known until after the election.

Some critics of Bird have insisted that the chief justice, aided by Tobriner, urged Manuel to remove his name from Clark's dissent and write one of his own for the purpose of delaying the final decision until after the election.

Bird and Manuel have yet to testify.