For more than a year, investigations of Enron Corp.'s massive collapse have dug into a web of partnership deals that allowed the company's executives to inflate earnings, hide debt and, in some cases, profit personally.

Now Enron's controversial and equally covert tax transactions are moving into the spotlight.

A court-appointed bankruptcy examiner has been investigating Enron tax deals as part of his broader inquiry into Enron's financial dealings, according to people involved in the inquiry. Enron records show that those undisclosed tax deals added more than $1 billion in "paper" profits to Enron's financial statements between 1996 and the company's bankruptcy filing in December 2001, helping it boost its stock price.

Examiner Neal Batson and his team of lawyers are seeking to recover for creditors any assets that Enron improperly transferred to outside partnerships. If he can show that tax or accounting rules were broken, he could claim assets involved in the deals or possibly sue the prominent banks and law firms that helped the Houston energy trader structure the complex transactions.

A report is due to be filed with U.S. Bankruptcy Court today, but it will not be made public until Feb. 14 at the earliest. A spokeswoman for the Atlanta lawyer would not answer questions about the report.

An even larger probe into Enron's tax strategies by the congressional Joint Committee on Taxation also is nearing completion. Sen. Charles E. Grassley (R-Iowa), chairman of the Senate Finance Committee, and Sen. Max Baucus (D-Mont.), the ranking Democrat, are preparing to hold hearings next month.

Armed with copies of Enron's tax returns, the joint committee will document the company's record just as Congress begins a broader debate on the fairness and effectiveness of federal tax policies, congressional sources say.

To Grassley and other critics, Enron was a prime example of a company that took advantage of the laws to avoid paying taxes.

In 2000, Enron's last full year of operation before its bankruptcy filing, it claimed revenue of $101 billion but paid just $34 million in U.S. taxes, according to Jim A. Seida, an accounting professor at the University of Notre Dame. The company's massive awards of stock-option benefits to executives created corporate deductions that wiped out $390 million in taxes that would have been due the Internal Revenue Service in 2000, Seida said.

A second issue for committee investigators is Enron's 11 "structured" tax deals, which the company did not need to cut its tax bills but did use to boost reported income. Like Batson's team, the committee is probing the role played by leading banks, law firms and accounting firms in designing and approving the deals.

Bankers Trust, now part of Deutsche Bank, was the most important of the firms that developed intricate, tailor-made tax-reduction strategies for Enron and other major corporate clients, according to Enron records provided to the tax committee and Batson's team.

Enron's former top tax counsel, Robert J. Hermann, who provided reports on the tax transactions to federal and congressional investigators and The Washington Post last year, said the deals did not violate tax rules.

"The government is not going to like these deals," he said in an interview last year. "People can disagree on what works within the written rules. . . . If you know the rules, you don't have to break the rules, you just use them. That's what lawyers and accountants do."

Some tax experts say that even if Enron's transactions followed tax law, they may have helped Enron paint a false picture of its profitability. The detail Enron disclosed about its tax strategies on its financial statements was so meager that average investors could not tell how much of its reported profits were coming from operations as opposed to one-time tax and accounting transactions, some experts say.

"An outsider doesn't see nearly enough detail to know what's going on. Even tax enforcers don't have a clear path laid out," said George A. Plesko, a Massachusetts Institute of Technology professor of management.

"It's a black box," Seida said.

The lack of adequate disclosure of corporate tax strategies is pervasive, according to Jeffrey Gramlich, a University of Michigan professor. He is calling for more detail on corporate tax calculations, or even a requirement that parts of corporate tax returns be made public.

One tax transaction Batson's team has scrutinized, according to one source, is a 1997 deal code-named Steele, in which Enron transferred a lease on corporate aircraft and other assets into a "special-purpose entity." An intricate series of loans and swaps of cash and stock produced large tax losses and deductions extending over a number of years. Each dollar of taxes saved added a dollar to profits, and Enron used the tax deal to add $66 million to its reported earnings between 1997 and 2001.

Another transaction, named Teresa, was designed to raise the value of Enron's investment in its Houston headquarters building by $1 billion, primarily through an inter-company loan, Enron documents show. That added $229 million to Enron's profit over 1997-2001. Bankers Trust was Enron's principal financial partner on both transactions, the records show.

Before going ahead with these transactions, Enron had to obtain what are called "should" letters from law firms saying that the tax deals were very likely to be approved by the IRS in case of an audit.

Susan P. Koniak, a Boston University Law School professor and ethics expert, said lawyers' roles in such deals should be closely examined. "You can't have structured finance without lawyers at the table. They're there every step of the way. They know where the line is," Koniak said of the lawyers involved in the Enron deals.

King & Spalding, an Atlanta-based law firm known for its tax expertise, received a $1 million fee for helping to design and then providing a "should" letter on the 1997 Teresa deal.

Former King & Spalding lawyer William F. Nelson said that he and colleague William S. McKee, who oversaw the Teresa transaction, said he could not discuss the case but that they stand by their judgments. According to Hermann, the fee King & Spalding received was not based on its willingness to give Enron a favorable opinion.

"We don't give tax advice that is incorrect at any time," added Nelson, who joined with McKee to form McKee Nelson LLP, a District-based firm specializing in tax issues. "If a client has a question, we answer it. . . . We don't come up with tax structures and go around looking for someone to buy them."

A spokeswoman for Akin Gump Strauss Hauer & Feld LLP, which provided the "should" letter on Steele, declined to comment on the firm's work for Enron, as did representatives at Deutsche Bank.