California prosecutors have begun to refuse plea bargains, use previously illegal evidence and tell juries about defendants' criminal records in the most sudden and extensive toughening in decades of any state's justice system.

The unprecedented shift in the balance of power toward the prosecution here has come in the wake of passage of Proposition 8, the "victims' bill of rights," with 56 percent of the vote June 8. Lawyers decrying the measure as an attack on civil liberties have already challenged its constitutionality in court, but prosecutors meanwhile are using many of the new weapons the omnibus proposition provides them.

Some say they fear, however, that an appeals court later could strike down some of Proposition 8's provisions, and force them to retry hundreds of cases at a cost of millions of taxpayer dollars.

Proposition 8 encompasses a series of changes in state law and the state constitution. It allows use of "the most relevant evidence," even if declared illegal in previous court decisions, and in serious cases forbids plea bargaining, a process in which lighter sentences are traded for guilty pleas to avoid time-consuming trials. It allows use of prior convictions to discredit testimony of witnesses in the eyes of the jury and establishes a victim's right to restitution from a criminal.

It also grants students and teachers the "inalienable right" to safe schools, adds five years to the prison terms of second offenders, abolishes the "limited capacity defense," limits the insanity defense and allows victims' families to testify at parole hearings.

"They threw everything in including the kitchen sink," said Edward Dent, a Virginia political consultant considered an expert on citizen-initiated ballot measures. As far as he knew, Dent said, Proposition 8 is the most far-reaching anti-crime measure ever passed by state ballot, but he said he is not certain it will survive review by the state or the U.S. supreme courts.

One of the first California defendants to feel the bite of Proposition 8 was Anthony Gonzalez, a Redwood City gardener convicted earlier this month of attempted murder after his brother was shot six times during an apparent argument. Gonzalez testified he was nowhere near the shooting and a friend took the stand to back him up, but San Mateo County prosecutors then revealed to the jury that Gonzalez had been convicted of child molesting in 1978 and his friend convicted of selling marijuana in 1964.

The criminal record disclosures, defense attorney John Digiacinto said, "had to have affected" the jury's decision to convict his client. Under California rules in effect before Proposition 8, the judge probably would have forbidden use of the criminal records because they were likely to prejudice the jury against Gonzalez without adding much relevant information to the case. But Proposition 8 restored the old common law rule--rapidly losing ground throughout the United States--that all felony convictions can be mentioned in court.

Digiacinto said the use of the prior records gives him a useful issue on which to appeal the conviction. His is only one of a number of expected appeals that UCLA law professor Norman Abram said should "tie up the courts in knots for years."

"We are not suffering a severe backlog, so we could absorb the cases if they were reversed," said San Mateo County assistant district attorney Stephen Wagstaffe. "But there are other counties that just couldn't take the six months' worth of reversals, of cases that would have to be retried."

George Nicholson, a former assistant state attorney general and this year's Republican candidate for attorney general, helped draft Proposition 8 along with Paul Gann, co-author of California's landmark tax-cutting measure, Proposition 13. Nicholson said Proposition 8 offered a means to steer courts away from overattention to the rights of criminals and back to more concern to the rights of victims. Asked how California could expect to make so many changes in its criminal justice system so quickly, Nicholson quoted the late Supreme Court Justice Louis D. Brandeis as saying, "A single courageous state, if its people so desire, can act as a laboratory."

Some local prosecutors said they began to comply immediately with the proposition's requirement that in 25 specific felony crimes they not plea bargain.

But others were reluctant to use some of the heavier guns in the victims' bill artillery, including the elimination of the "exclusionary rule," which had barred evidence obtained through warrantless and other illegal searches, and the allowance of prior felony convictions introduced in court.

In one Santa Clara County case, using criminal records appeared to backfire. A jury acquitted two men charged with having stolen guns in their car after the pair's lengthy prior records were revealed in court. Some jurors said afterward that they could not believe such experienced criminals would have been so careless.

Jeff Brown, the elected public defender in San Francisco, said the city's prosecutors were refraining from using the new rules that might be overturned on appeal if they felt they could win cases with the old rules. "They don't want to endanger any conviction if they've got the guy dead to rights," Brown said. Leo Himmelsbach, assistant district attorney for Santa Clara County, said if prosecutors decided they could not get a conviction in the case without using some of the Proposition 8 rules, "We're going to go for that."

A suit filed by two prominent lawyers and the president of the California Teachers Association in the San Francisco Court of Appeals asks that Proposition 8 be struck down because it violates a constitutional provision limiting ballot measures to a single subject.

State Attorney General George Deukmejian asked the state's Supreme Court to take up the issue immediately and avoid a long delay that could require hundreds of cases to be retried if the proposition were overturned. Some politicians here have suggested, however, that the court, already under heavy political fire for some pro-defendant decisions, may be reluctant to decide such a matter before November, when the terms of four of its members are up for a vote.