Investigators for the Senate Governmental Affairs subcommittee on investigations have been authorized to provide testimony against three former executives of Enron and Merrill Lynch who are scheduled to face trial later this month for making false statements to a Congressional committee.

Dan Boyle, a former vice president in Enron’s global finance unit, has been formally charged with making a false statement to a Congressional committee. Two other defendants who worked for Merrill Lynch were accused of making false statements to the same Senate panel but were not formally charged with that offense in an augmented indictment late last month.

The three executives, along with three other defendants, are charged with wire fraud and other offenses arising from what prosecutors called a sham accounting transaction involving Nigerian power-producing barges.

In resolutions approved in June and July, the Senate approved providing documents and testimony in the case following a 2002 investigation by the subcommittee.

The panel, then under Democratic control, conducted a seven-month probe that concluded that Merrill Lynch had assisted Enron in cooking its books by pretending to purchase an existing Enron asset when it was really engaged in a loan.

The subcommittee’s investigation concluded that the accounting sham involved the sale of an interest in three Nigerian barges that operated as floating power stations. Enron wanted to sell these barges before the end of 1999 so it could report the sales income as earnings in its 1999 financial statements, but Enron was unable to find a buyer.

In mid-December 1999, Enron asked Merrill Lynch to set up a special-purpose vehicle, subsequently called Ebarge, to take an Enron asset — in this case, barges, or the income that they might create — for a short period of time and for a $28 million purchase price that consisted of a $7 million cash payment from Merrill Lynch and what has been characterized as a loan of $21 million from Enron to Ebarge. This transaction would allow Enron’s African division to book sales income of $12.5 million.

Merrill Lynch agreed, but only after receiving Enron’s commitment that it would find a buyer for Merrill Lynch’s interest in the barges within six months. Merrill Lynch also received assurances of a 15 percent return on its $7 million, plus an immediate payment of $250,000.

On the day before the deadline, LJM2, an investment vehicle run by Enron’s former chief financial officer, Andrew Fastow, stepped in and took over an interest in the barges from Merrill Lynch at the previously agreed-upon terms. It paid Merrill Lynch the $7.525 million that had been assured to Merrill by Enron at the beginning of the transaction, and it assumed the $21 million note Enron initially loaned to Ebarge.

On July 19, 2002, according to the indictment, the subcommittee staff interviewed Boyle concerning the barge transactions.

The indictment charged that Boyle allegedly made false statements on a material matter by testifying, among other things, that he did not know of any oral promise or guarantee between Enron and Merrill Lynch relating to the barge transaction.

Two former Merrill Lynch employees, Robert Furst and James Brown, were also said to have provided false statements to Senate investigators about the Nigerian barge transactions, according to the indictment.

Charles Tiefer, a former solicitor for the House and author of the upcoming book “Veering Right: How the Bush Administration Subverts the Law for Conservative Causes,” said false statements to Congress are often included as part of the fact pattern in indictments but are often not formally charged.

But if prosecutors believe they can successfully prove such a charge, they may decide to tack it on to an indictment.