WASHINGTON (Reuters) - Investigators looking into alleged U.S. Secret Service misconduct in Colombia before President Barack Obama's trip there must probe how often this has happened before, the Republican chairman of a House government oversight panel said on Sunday.Representative Darrell Issa also told CBS' "Face the Nation" program that there may have been more agents involved than the 11 who were sent back to Washington after allegations surfaced that they had brought prostitutes to their hotel in Colombia.
But this was rejected by a Secret Service spokesman, who told Reuters he had no information that more than 11 of the agency's personnel had been implicated.
Agents whose job it is to protect the president and other Cabinet members could be blackmailed by the kind of activity that has been alleged, said Issa, chairman of the House Oversight and Government Reform Committee.
Issa, a frequent critic of the Obama administration, said he has not decided whether to have committee hearings on the scandal.
"The investigation will not be about the 11 to 20 or more involved, it will be about how did this happen and how often has this happened before," Issa told CBS. "Things like this don't happen once if they didn't happen before."
The Secret Service said on Saturday that it had put 11 agents on administrative leave to investigate their behavior ahead of the Colombia summit, and apologized for the distraction the incident had caused.
Assistant Director Paul Morrissey said in the Saturday statement that the Secret Service replaced the agents after allegations were made on Thursday, in line with the service's "zero tolerance" policy on personal misconduct.
The Secret Service gave no details about what may have occurred in Cartagena, a coastal city hosting the 33-nation Summit of the Americas. Obama arrived in Cartagena for the conference on Friday and was staying through Sunday.
A local Colombian police source said that agents had brought prostitutes back to their hotel.
A U.S. source familiar with the situation told Reuters that it appeared some of the agents allegedly involved had gone to a bar and brought back various friendly women who turned out to be asking for money when they got back to the hotel rooms.
Five military servicemen, assigned to support the Secret Service during Obama's visit, have also been implicated in the incident, which has become a major embarrassment for Washington at the summit.
Issa said incidents like this could pose a danger to the president. "In this particular case, the president may not have been in danger, but that's to beg the whole question of - What happens if somebody, six months ago, six years ago, became the victim of their own misconduct and is now being blackmailed?" he said.
"It's not about whether the president was in danger this time. It's whether or not you need to make changes so the American people can have confidence" in the agency, Issa said.
He wanted to know how they would make changes in discipline, perhaps involving polygraph tests, to prevent a recurrence, he said.
Morrissey said on Saturday that the personnel involved were special agents and uniformed division officers, none of whom were assigned to the presidential protective service. All were interviewed at Secret Service headquarters in Washington on Saturday.
(Reporting By Susan Cornwell; Additional reporting by Mark Hosenball; Editing by Eric Beech and Sandra Maler)