Criminal investigators examining the Enron Corp. debacle have expanded their inquiry to focus on activities at the commercial banks that provided billions of dollars in loans and other financial services to the company, according to current and former Enron executives and others involved in the investigation.

Federal prosecutors are investigating whether individual bankers illegally benefited from deals involving Enron-related entities, potentially at the expense of their employers, people involved in the case said.

A number of bankers have been questioned about such self-dealing, lawyers said, and the government is said to be weighing whether to bring charges in one such matter.

The government has also stepped up its examination of the Enron-related partnership Chewco. The financing for the partnership included loans from Barclays Bank that Enron's auditors have said, in congressional testimony, were structured in a way to hide them.

The discovery of the secret loans ultimately played a central role in the financial crisis last fall that led to Enron's collapse.

The Manhattan district attorney's office, working independently of the federal Enron task force, has opened an inquiry into an array of transactions and financial institutions tied to Enron.

According to current and former Enron executives who have been questioned by the Manhattan investigators, these include a series of deals between Enron and J.P. Morgan Chase that have been described in private lawsuits as disguised loans to the energy trader.

Investigators for the district attorney, Robert M. Morgenthau, have begun interviewing witnesses in Houston, where Enron is based. But Manhattan prosecutors do not appear to be close to bringing charges, people involved in the case said. There is no indication that the banks are targets of the inquiry.

Combined with the recent conviction of Enron's former accountant, Arthur Andersen, these latest lines of inquiry signal that investigators are putting the conduct of the company's financial advisers under a harsh light as they consider bringing charges of fraud and related crimes against Enron's former top executives.

Banks had complex financial relationships with Enron, the full details of which began to emerge only amid the debris of the collapsed company.

Like most companies, Enron borrowed money to finance its operations. But banks also provided cash for the company's off-the-books partnerships and for outside investors in those entities.

Some financial institutions and bankers were investors in the partnerships.

Major New York banks, meanwhile, engaged in circular trades with Enron that allowed the company to obtain billions of dollars in loans without disclosing them to shareholders.