A federal judge ruled yesterday that e-mails from a J.P. Morgan Chase & Co. official referring to "disguised loans" may be entered as evidence in a civil trial, supporting allegations that the company helped Enron Corp. conceal its growing debt before its collapse.

U.S. District Judge Jed S. Rakoff had initially kept the memos by Chase Vice Chairman Donald Layton to others within the financial giant away from the jury, saying their impact could be "explosive." But yesterday he admitted them after reviewing the issue.

The trial in Rakoff's New York City courtroom involves a commercial dispute between Chase and a group of insurance companies. But the ruling also helps attorneys for former Enron shareholders, who hope to expand their class-action lawsuit against Enron's former top executives to include the Houston company's deep-pocketed bank lenders and legal advisers. The shareholders' attorneys have made the same claim -- that complex securities transactions known as "pre-pays" by Chase and other financial institutions enabled Enron to hide its true indebtedness.

Last week, U.S. District Judge Melinda Harmon in Houston gave shareholders' attorneys the right to seek documents and testimony from banks and law firms to support their case.

Over the decade, Chase raised $3.7 billion for the Houston company in return for Enron's promise to make future deliveries of oil and natural gas. The transactions were counted as energy trades on Enron's books.

According to a Senate investigations subcommittee, the deals were really loans, steered through an offshore company called Mahonia Ltd. that the subcommittee said Chase controlled. Chase officials insist that Mahonia, based in the Jersey Islands, is independent and that the transactions were true commodity trades.

Chase purchased $1 billion in surety bonds from 11 insurance companies, including Liberty Mutual Group, Chubb Corp. and CNA Financial Corp., as protection in case Enron didn't make good on its commitments. But when Enron failed a year ago, the insurance companies refused to pay, contending that they had been deceived, and Chase sued to compel payment.

In May 1999, Layton wrote an e-mail about the bank's use of prepaid commodity transactions: "We are making disguised loans, usually buried in commodities or equities derivatives (and I'm sure in other areas). . . . I am queasy about the process."

In the trial last week, Layton told the court out of the jury's presence that he was trying to make sure the bank was following proper internal precautions with such loan-like cash advances. There was no intent to disguise transactions from outsiders and none of his 1999 e-mails referred to Enron transactions, Layton said, adding that he did not learn about Mahonia until Enron's bankruptcy filing.

"Mr. Layton's comments are a red herring. They do not in the least support the theory being argued by the insurance companies in this case," Chase spokeswoman Kristin Lemkau said yesterday.

"What the [shareholder] plaintiffs want to show is that Enron, its lawyers and especially its bankers knew these transactions were bogus," said Robert Prentice, a professor of business law at the University of Texas. "It's extremely embarrassing for the banks if they characterized them as bogus."

The banks' pre-pay transactions with Enron are being investigated by the Justice Department, the Securities and Exchange Commission and by a grand jury under Manhattan District Attorney Robert Morgenthau.