Federal regulators and prosecutors are listening to tape recordings of more than 150 Riggs Bank board meetings as they investigate what role top executives, including former chairman Joe L. Allbritton, played in more than a decade of violations of anti-money-laundering laws at the company, according to five sources familiar with the tapes.

Despite earlier requests from regulators and Senate investigators for documents related to the violations, the bank did not discover the more than 125 tapes until recently, the sources said. The tapes are of board meetings at the bank and its holding company beginning at least as far back as 1989 and ending some time last year, according to the sources, who spoke on condition that their names not be used because of ongoing civil and criminal investigations.

On the tapes, Allbritton, who left Riggs's holding company board in May but remains its largest shareholder, makes what one source said were "derisive" remarks about federal bank regulators who were pushing the bank to correct years-long violations of money-laundering laws. Neither transcripts nor copies of the tapes were made available.

Recording and archiving conversations of board meetings is unusual, corporate legal experts say, because of the potential such recordings could be used against the company or its directors in a legal proceeding. Written minutes, often sanitized of colorful statements or even give-and-take among directors, are usually the only records kept of what board members say to one another.

Yet Riggs meetings were routinely recorded under Allbritton's direction, the sources said. While directors were informed once a year that their conversations could be recorded, a source familiar with the board said several directors expressed surprise that the recordings existed.

The recordings, stuffed in a box in Allbritton's Riggs office along with a cache of photographs of Allbritton with various associates and clients of the bank, were stumbled upon at the end of July by an employee who worked for Allbritton, according to sources. Sources also said Allbritton has hired a lawyer from Skadden Arps Slate Meagher & Flom LLP to represent him in connection with the investigations.

Riggs spokesman Mark N. Hendrix yesterday confirmed the existence of the tapes.

"To facilitate the keeping of the minutes of board meetings, Riggs has recorded its board meetings," he said. "Consistent with information requests, Riggs has provided the recordings to its regulators."

Paul Clark of Hill & Knowlton Inc., a spokesman for Allbritton and his son Robert, now chairman of the bank and its holding company, did not return repeated calls seeking comment on why Allbritton didn't disclose the existence of the tapes to federal investigators, including the U.S. attorney in the District, until a few weeks ago.

Failure to turn over the tapes sooner has angered federal investigators, including those working for the Senate permanent subcommittee on investigations. For over a year, the subcommittee has been probing Riggs and its relationship with customers such as former Chilean dictator Augusto Pinochet, Saudi Arabian Embassy officials and the presidentof Equatorial Guinea.

After the terrorist attacks of Sept. 11, 2001, bank regulators and the FBI began a detailed probe of Riggs Bank's long-standing relationship with officials at the Saudi Embassy. That evolved into multiple federal investigations, including one by the Justice Department, of the bank's relationship with other foreign customers, including inquiries into deposits by major U.S. oil companies into accounts controlled by Equatorial Guinea's president, Teodoro Obiang Nguema.

In May bank regulators at the Treasury Department fined Riggs $25 million for violations of the Bank Secrecy Act, which has been in effect since the 1970s but was strengthened in the fall of 2001 to bolster efforts to interrupt financing of terrorist operations.

Earlier this summer, the Senate subcommittee held a hearing on Riggs that publicized for the first time what investigators called evidence that the bank helped Pinochet hide millions of dollars from international prosecutors over the past decade. Prosecutors in Spain and Chile have sought information about that money as possible restitution for families of thousands of victims Pinochet is alleged to have tortured and killed while president of Chile.

The connection with Pinochet touched off wider investigations by bank regulators and Justice Department prosecutors.

Federal bank regulators asked in May for all records concerning Joe Allbritton and the bank, a request that within weeks was joined by the Justice Department as part of a criminal investigation.

When Allbritton's employee found the tapes, the employee notified the bank's general counsel, Joseph M. Cahill, who in turn notified the bank's outside counsel at the New York law firm of Sullivan & Cromwell LLP, sources said.

Those lawyers then notified federal officials, asking for time to get the tapes organized and transferred to CDs before turning them over to the government, which the bank began to do Aug. 10. When Riggs's attorneys last month briefed the Senate subcommittee investigators about an internal Riggs probe of its Pinochet connection, they disclosed the existence and content of the tapes, sources said.

In a related matter, yesterday the ranking members of the Senate subcommittee, Carl M. Levin (D-Mich.) and Norm Coleman (R-Minn.), said they would introduce legislation Monday to require a "cooling off" period for senior bank examiners, barring them from working for banks they directly regulate for one year after they leave their government jobs.

In their July hearings on Riggs, Levin and Coleman were sharply critical of R. Ashley Lee, Riggs's former chief federal bank examiner, for going to work as a senior executive at Riggs a few days after retiring from the Office of the Comptroller of the Currency. Last month Comptroller John D. Hawke Jr. called for such legislation.

Joe L. Allbritton, former chairman of Riggs, had all board meetings recorded.