In November 2001, Daniel E. Berce's private banker offered him a way to avoid $3 million in taxes he owed after cashing in a large block of stock options.

Berce had good reason to trust the Dallas-based banker. Bank One had been his personal bank for 18 years. Bank One was also a major financier to AmeriCredit Corp., the huge Fort Worth-based auto lender. At the time, Berce was AmeriCredit's chief financial officer -- and the company's good fortunes had made him a millionaire.

The bank offered Berce a way to not pay taxes on some of those millions. It was called Homer and was a tax-sheltering foreign currency transaction (named after the "Simpsons" character) that all but eliminated Berce's stock option gains. The problem is that Homer was a sham, according to government sources, lawyers familiar with the case, and lawsuits by Berce and several other wealthy business people.

The Berce case and others, as described in state and federal court filings, highlight the central role U.S. banks have played in the unfolding tax shelter scandals. While accounting and investment firms devised the shelters, banks helped promote and sell them. Accounting firm KPMG LLP on Monday agreed to pay $456 million and to cooperate with authorities investigating tax shelter deals. Rival Ernst & Young LLP remains under grand jury investigation for its role in selling shelters.

But experts say about a dozen major financial institutions with divisions that cater to the super-wealthy were in most cases the point of entry for tax shelter promoters, and federal investigators are expanding their probe to the role that bankers, financial advisers and lawyers played. Often, lending institutions such as Wachovia Corp. referred their wealthy clients to promoters selling what the Internal Revenue Service says are invalid shelters. In other cases, experts at such institutions as Bank One and Bank of America devised and sold questionable tax avoidance strategies themselves.

The IRS has estimated that tax shelters promoted by those banks and others improperly shielded more than $8 billion in income from federal taxes.

The fees for providing such tax-avoidance strategies were substantial. Berce paid Bank One and the co-promoters of Homer -- Jenkens & Gilchrist PC and Deutsche Bank AG, the German bank that made billions of dollars of "loans" to make the deals work -- $350,000 in fees. And Berce, now AmeriCredit chief executive, was not the only AmeriCredit insider who bought into Homer. AmeriCredit director James H. Greer, owner of a Houston building products company and also a client of Bank One, paid $600,000 in fees for a Homer in an attempt to avoid $5 million in taxes on AmeriCredit stock options.

Both men were told by the IRS in 2004 to amend their tax returns for 2001 and pay interest and penalties, according to their lawsuits against Bank One.

Bank One was acquired last year by J.P. Morgan Chase & Co. Bank spokesman Tom Kelly declined to comment on any of the pending lawsuits against the company because the cases are in litigation. A Deutsche Bank spokesman declined to comment.

The first person indicted in the ongoing federal investigations into the tax shelters was a banker, not an accountant. The plea by former HVB Group official Domenick DeGiorgio to conspiracy, fraud and tax evasion charges was the first time an individual involved in abusive tax shelters characterized them publicly as sham transactions designed to subvert the law.

"Our self-reporting tax system cannot tolerate the fraudulent acts of bankers, accountants and lawyers who, under the guise of 'sophisticated tax planning,' create elaborate structures that have no purpose but to mislead and defraud the IRS," U.S. Attorney David N. Kelley said at the time.

The deals broke the law, DeGiorgio said in court, because they were investments that involved little or no credit risk and because they were intended to produce tax losses. To comply with the tax code, investors must reasonably expect they will make a profit on such deals.

Language in a conspiracy indictment of eight former KPMG officials announced Monday refers to four unnamed, international banks that helped wealthy clients take part in the shelters.

Investigators at the Senate permanent subcommittee on investigations issued a report in April that first chronicled the role of bankers, lawyers and accountants in marketing the shelters. HVB earned $5.45 million for its role in 1999 alone. Deutsche Bank reaped $79 million in fees for BLIPS, another tax shelter, and earlier deals called OPIS, the Senate report said.

Bank of America, the largest U.S. bank, about six years ago began offering a tax shelter under the brand STARS. Texans Charles and Sam Wyly, who made several hundred million dollars as entrepreneurs in the software and retail industries in the past 20 years and who control Michaels Stores Inc., a chain of craft stores, were among their customers.

According to Securities and Exchange Commission filings, the brothers sought to avoid taxes on stock options by transferring the options to an offshore family trust. Bank of America sold the Wylys a deal that allowed the trusts to then convert the options into cash, without paying any taxes.

A Bank of America spokeswoman declined to comment on the Wyly case but said STARS is a form of derivative product commonly marketed by all banks and investment broker dealers to lock in profit on stock options.

The IRS said earlier this year that the shelters of the type employed by the Wylys with Bank of America's assistance helped shield from taxes $900 million in income from hundreds of wealthy business executives.

Lawsuits against Bank One detail the close relationship of law firms, accountants and tax advisers with the bank that sold invalid tax shelters to its clients. The bank's wealth management division in Chicago had an Innovative Strategies Group to come up with novel tax avoidance strategies for wealthy clients. Two of the executives in the group were former national tax group members of KMPG. Both men, along with most of the rest of the Innovative Strategies Group that designed Homer in 2001, have since left the bank, according to a source at the bank who spoke on the condition of anonymity because of the pending litigation.

Lawmakers who examined the tax shelter industry said lending institutions and others require heightened scrutiny to ensure they do not promote illegal tax shelters. Sens. Carl M. Levin (D-Mich.) and Norm Coleman (R-Minn.) introduced a bill last month that would increase penalties for knowingly aiding or abetting taxpayers to minimize their bills. The legislation also would require federal bank regulators to develop ways to detect tax-related violations by banks and to review those strategies at least every two years.

"Our bill provides our government the tools to end the use of abusive tax shelters . . . and to punish the powerful professionals who push them," Levin said.

Former banker Domenick DeGiorgio pleaded guilty to charges linked to tax shelters.