More than 850 alleged victims are suing dioceses throughout the state, with millions of dollars in potential settlements at stake in a legal battle that involves more than 300 attorneys and dozens of church insurers. The scope is so vast that the lawsuits have been lumped geographically into three consolidated cases, known simply as Clergy I, Clergy II and Clergy III.

After nearly two years, the pace of the complicated legal drama is about to accelerate with the first significant steps toward possible resolution.

Several developments promise to propel the cases forward: Trial dates were set last week for a handful of Northern California cases; a key court hearing on public access to internal church documents is set for Wednesday; and Cardinal Roger Mahony of Los Angeles, leader of the nation's largest archdiocese, is expected to be deposed by year's end in cases related to his tenure in the Stockton and Fresno dioceses.

Legal analysts and attorneys agree that the developments, all of which involve Northern California cases, will affect settlement negotiations that have dragged on for months in Southern California. Exactly what those impacts will be is less certain.

Trials in a handful of Northern California cases, scheduled for March, May and June, could prompt settlements. Others say a few multimillion-dollar jury verdicts could have a chilling effect on the ongoing talks by giving other plaintiffs inflated expectations and exhausting church resources.

''Depending on the circumstances, trials could bust loose settlements or it could lock the church in,'' said Stephen Yeazell, a law professor at the University of California, Los Angeles, who specializes in complex civil litigation. ''It's going to change the calculus no matter what.''

But attorneys for the Los Angeles archdiocese, which faces about 490 civil cases, said it would take more than a handful of trials to discern a pattern that would shape a settlement.

The dioceses involved in the Southern California talks -- Los Angeles and Orange (Clergy I), and San Bernardino and San Diego (Clergy II) -- account for more than 80 percent of all clergy-abuse lawsuits filed statewide.

''Any cases that are tried that result in a verdict give us some idea of what a particular jury thinks a particular case is worth,'' said Don Woods Jr., Los Angeles archdiocese attorney. ''But one case out of a thousand isn't worth very much.''

In the two years since Cardinal Bernard Law of Boston resigned at the height of a clergy abuse crisis there, California has emerged as the nation's new epicenter of the scandal that has shaken the Roman Catholic Church.

Much of the attention results from a 2002 state law that temporarily suspended the statute of limitations for filing molestation lawsuits, opening the door for hundreds of claims. The number of cases filed against the Archdiocese of Los Angeles alone is just slightly less than the number filed in Boston, where the archdiocese settled with more than 550 plaintiffs for $90 million.

''In some respects, I think this is the most complex case that state courts have had to deal with,'' said Ray Boucher, the lead attorney in Southern California. ''It is really unique to have the confluence of potentially explosive cases in one location against such a limited number of defendants -- essentially one.''

Attorneys and legal experts compare the clergy abuse claims to the asbestos litigation that swept the nation in the 1970s and 1980s, when tens of thousands of people sued over exposure to asbestos that dated back decades.

As in the church cases, those claims involved allegations that spanned years and involved many witnesses and defendants who had since died. But unlike the church-abuse cases, an asbestos claim could be verified with a lung X-ray.

J. Michael Hennigan, a Los Angeles archdiocese attorney, described some of the clergy claims as ''silly,'' such as the person who sued because a priest blew in their hair.

The judge supervising the 160 clergy abuse lawsuits in Northern California (Clergy III) has kept his docket on a steady march toward trial, while in Southern California the nearly 700 cases entered a closed-door mediation process nearly two years ago. The difference in approach was necessary because of the sheer number of cases in Southern California, Boucher said.

Yet in clearing a path for trial in Northern California in recent months, Alameda County Judge Ronald Sabraw has ruled on key constitutional questions that touch on tenets central to all California clergy-abuse litigation.

The rulings ''set up parameters for everything'' that could be instructive elsewhere, said Stephen McFeely, attorney for the Oakland diocese.

The most important question challenges the constitutionality of the state law that opened the door for the deluge of lawsuits. If the law were found unconstitutional, the nearly 860 claims statewide against the church could be thrown out.

Church attorneys say the law unfairly targets the Catholic Church and was drafted by the same trial lawyers now hired by plaintiffs to press their cases.

In July, Sabraw ruled that the state law was constitutional in almost all cases and allowed all but a handful of the Northern California claims to go forward.

''It's a huge ruling. There were open questions in California law on these precise issues, and this resolved them all,'' said Marci Hamilton, a professor at Cardozo Law School at New York City's Yeshiva University, who assists the plaintiffs' legal team. ''It may well have a persuasive effect. The reasoning Sabraw used was strong, and it's hard to disagree.''

The Diocese of Davenport, Iowa, has challenged the same law in federal court in San Diego, where it was sued because one of its priests allegedly molested a parishioner in that city in the 1960s. The Archdiocese of Los Angeles attempted to join that challenge but was denied.

The Iowa diocese will pursue the challenge without Los Angeles, said Susan Oliver, a San Diego-based attorney for the Davenport diocese.

''The statute is unconstitutional, and it certainly is unconstitutional as applied to this particular client,'' Oliver said. ''It violates due process and it violates church autonomy doctrine.''

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Central to the litigation is whether confidential church records about individual priests are protected under the First Amendment. The documents are being sought by both plaintiffs' attorneys in the civil lawsuits and by the Los Angeles County district attorney's office in a criminal investigation.

The church describes the documents as confidential communications between a penitent and a confessor and says they are protected by the constitutional guarantee of freedom of religion.

In September, a retired state judge appointed as a special master in the Los Angeles case rejected archdiocese arguments and ordered it to turn over about 480 pages of communications between the priests, their bishop and church counselors. Psychological reports are exempted.

Church attorneys plan to appeal, a process that could take years.

In a civil ruling, Sabraw in early August ordered the confidential documents on accused Northern California priests turned over to plaintiffs' attorneys. The next day, the judge placed a temporary seal on the documents to prevent the attorneys from making them public.

That order expires Wednesday. Media attorneys representing the New York Times Corp. and the San Francisco Chronicle will ask Sabraw to give their clients access -- a move that could prove devastating for the church.

In 1998, attorneys used a similar confidential file as evidence in a jury trial against the Diocese of Stockton. The jury returned a verdict of $30 million -- later reduced to $7.5 million -- based largely on documents in the file that indicated the diocese knew of allegations against the priest but nevertheless shuffled him from parish to parish.

Paul Balestracci, an attorney for the Stockton diocese, said he worried the public would distort information should it become available.

''There's the sensationalism about the cases in general and that's a big issue,'' he said.

The advance of the Northern California cases toward trial has had another unexpected consequence: Cardinal Mahony in Los Angeles has been ordered to give a deposition about his knowledge of accused priests who worked decades ago in Fresno, where he was auxiliary bishop, and Stockton, where he was bishop.

Mahony also can be questioned about general policy followed in Northern California dioceses on clergy abuse reports during that time.