WASHINGTON — Billions of dollars in U.S. taxes are going unpaid because Americans are exploiting Swiss bank accounts, and the U.S. government has failed to aggressively pursue Switzerland’s second-largest bank, a Senate investigation has found.

The bank, Credit Suisse, has provided accounts in Switzerland for more than 22,000 U.S. clients totaling $10 billion to $12 billion, according to a report issued Tuesday by the Senate Permanent Subcommittee on Investigations. The U.S. government has received only 238 names of U.S. citizens with secret accounts at Credit Suisse, or just 1 percent of the estimated total, the investigation concluded.

Credit Suisse recruited U.S. clients to open Swiss accounts from 2001 through 2008, helped them conceal the accounts from the Internal Revenue Service and enabled misconduct by bank employees, the subcommittee asserted.

For five years, the Senate panel has been examining Swiss banks’ use of secrecy laws to enable tax evasion by Americans. The main focus of its latest report was Credit Suisse.

Credit Suisse had no immediate comment on the Senate report.

Responding to the report in a statement, the Justice Department said it is investigating up to 14 Swiss financial institutions, “and we won’t hesitate to indict if and when circumstances merit.” It did not name the banks.

The Senate subcommittee asserted that the Swiss government, with its famous banking secrecy, has continued to obstruct U.S. authorities’ ability to learn the names of U.S. bank customers and former customers.

The report detailed cloak-and-dagger tactics used by Credit Suisse bankers who were said to travel to the United States to secretly service accounts and recruit customers – including at golf tournaments in Florida and the annual “Swiss Ball” in New York.

Over breakfast at a hotel, one banker handed a U.S. customer bank statements hidden in a Sports Illustrated magazine, the report said. The bank filed visa applications for employees that falsely portrayed them as tourists and maintained a New York office.

Credit Suisse “aided and abetted U.S. tax evasion, not only from behind a veil of secrecy in Switzerland, but also on U.S. soil by sending Swiss bankers here to open hidden accounts,” Sen. Carl Levin, D-Mich., the subcommittee’s chairman, said at a news conference Tuesday.

Levin said the Justice Department has failed to use the U.S. legal tools with Credit Suisse that were used earlier to pry the names of U.S. account holders from No. 1 Swiss bank UBS. The Justice Department has instead used treaty requests for the names, relying on Swiss courts and getting stymied, he said.