By Susan Cornwell and Tabassum Zakaria

WASHINGTON (Reuters) - The U.S. Secret Service is examining a new report of alleged misconduct by agents at an El Salvador strip club ahead of a trip there last year by President Barack Obama, a senior lawmaker said on Thursday.

Representative Peter King, a Republican who chairs the House Homeland Security Committee, said in a statement to Reuters that the review is part of an extensive investigation the Secret Service is conducting in the aftermath of an incident involving prostitutes in Columbia.

U.S. State Department spokeswoman Victoria Nuland told reporters the agency also is looking into the El Salvador allegations, aired Thursday in a report by Seattle channel KIRO-TV, part of the CBS-Cox media group.

In the television interview, an anonymous U.S. contractor described visiting a club offering sexual favors with some Secret Service agents and U.S. military specialists in advance of Obama's March, 2011, visit.

"Obviously, we will inquire of our embassy in San Salvador with regard to the conduct of our own employees. But the article alleges that they attended the establishment, not that they engaged in any illegal or unsanctioned conduct," Nuland said.

Southern Command was looking into whether investigation of the allegations was merited, a spokesman said.

Interest in the El Salvador allegations came a day after U.S. Homeland Security Secretary Janet Napolitano assured lawmakers that no Secret Service misconduct similar to the recent carousing in Cartagena, Colombia, had been found in the last two and a half years.

ALLEGED MISCONDUCT FOR YEARS

Senator Joseph Lieberman, chairman of the Senate Homeland Security Committee, said Thursday he was disappointed to learn of the latest allegations.

"I keep running into people who say they have talked to agents who tell them of misconduct of this kind over the years," he said. Lieberman plans to hold hearings into whether there was a pattern of such behavior.

A Secret Service spokesman said Thursday the agency would pursue any "credible" information brought to its attention.

"The recent investigation in Cartagena has generated several news stories that contain allegations by mostly unnamed sources. Any information brought to our attention that can be assessed as credible will be followed up on in an appropriate manner," the spokesman said.

Napolitano said Wednesday that records kept by the Secret Service Office of Professional Responsibility showed no recent episodes similar to the events in Cartagena. Agents and military service members are accused of spending the night of April 11 partying at a bar before bringing up to 21 women back to hotels.

That episode was exposed the next morning when one woman complained she was not paid enough money. Twelve agents and 12 military service members were linked to the incident.

The Secret Service, which is attached to the Department of Homeland Security, has reviewed the cases of all 12 of its implicated agents.

Eight of them are now gone, three were cleared of serious misconduct, and one is being stripped of his security clearance, which would prevent the agent from working at the agency.

(Additional reporting by Arshad Mohammed and David Alexander; Editing by Marilyn W. Thompson and Philip Barbara)