Californians who dodged taxes by hiding their money in questionable tax shelters have coughed up more than $1 billion under the state's just-ended amnesty -- shattering national records.

The $1 billion reaped in the amnesty program surprised state leaders in a number of ways:

• It has raised more than twice as much money as any amnesty program in U.S. history.

• It is about 12 times more than the state originally anticipated -- and nearly four times the revised goal set just a week before the April 15 deadline.

• Fewer than 900 taxpayers tried to protect their money from taxes, but that equaled roughly 2 1/2 percent of all the personal and corporate income taxes that the state will collect.

But most important, it's evidence that tax-shelter abuses are costing cash-strapped states like California and the federal government far, far more than they knew.

``You begin to wonder if this is the tip of the iceberg,'' said Assemblyman Dario Frommer, D-Glendale, whose bill last year gave California the nation's toughest penalties for tax-shelter abusers. ``It does make you wonder whether there is large-scale cheating going on by some very wealthy and privileged individuals on these kinds of tax shelters.''

One thing is certain: The 4 1/2-month-long Voluntary Compliance Initiative exceeded everyone's expectations -- again and again and again. Originally, the state Franchise Tax Board figured it would net $90 million by the April 15 deadline. But it blew past that mark with more than a month to go. Just a week before the deadline, state officials raised the top estimate to $275 million, only to pass the $300 million mark by April 15.

Ever since, the number has climbed like a tote board at a telethon, hitting $838 million Thursday and eclipsing $1 billion by Monday. And the state has about 50 returns to count, not to mention an undetermined number of returns sent via certified mail.

``It's kind of fun,'' said Denis Azimi, spokeswoman for the state tax agency. ``You don't know what the next one will have.''

At $1 billion and counting, California's amnesty has shattered the $532 million mark set last year when Illinois offered amnesty to tax scofflaws of all varieties.

``It's a massive amount,'' said Joseph Bankman, a Stanford Law School professor who helped shape the state's legislation. ``It's one thing to get a half-billion or a billion from tens of thousands of taxpayers, but here you have less than 1,000 taxpayers and it's already over $1 billion.''

Because the tax agency is still focused on opening the mail and cashing the checks, it hasn't had time to analyze the program yet. But here are a few preliminary anecdotal nuggets, according to the tax board:

• The 296 corporate taxpayers tallied so far include companies in the oil and gas industry, financial services, retailing and even some large accounting firms. The average check from corporations is $1.3 million, but the uncounted number of companies with Bay Area ties each paid at least $25 million.

• The average check from individual taxpayers was $1.2 million, but some paid much more. So far, an unidentified Atherton taxpayer holds the Bay Area record with a check for $8.7 million.

• Most of the taxpayers paid up but sought to protect their appeal rights in hopes of winning refunds later. But about $264 million came in from taxpayers and businesses who waived their rights in order to close their cases.

The success of California's amnesty should serve as a national model, some experts say. Frommer and state Sen. Gilbert Cedillo, D-Los Angeles, laid the foundation with bills that gave California the toughest tax-shelter penalties in the nation. Last summer, California became the first state in the nation to agree to share leads with the Internal Revenue Service, an arrangement that soon yielded the names of 3,500 suspected cheaters in the state. And the tax board mailed 31,000 warning notices to taxpayers.

``Every state in the country should be watching what California has done here and should be thinking about their own programs,'' said Controller Steve Westly. ``Let's not forget virtually every state in the country has a budget crisis now.''

Although the amnesty has raised at least $1 billion to narrow California's $12 billion deficit, Stanford's Bankman says the state's biggest payoff might be yet to come.

``People won't do these shelters in the future,'' Bankman said. California is ``certainly the last place you'll be marketing these. It's like putting locks on the doors and hiring policemen. The promoters will go elsewhere.''