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Conflicting portraits of the Secret Service took stage Wednesday on Capitol Hill, as senators challenged Homeland Security Secretary Janet Napolitano to reconcile the image of agents who protect the lives of America's president with the dozen officers and supervisors implicated in a humiliating prostitution scandal.

Napolitano told the Senate Judiciary Committee that the incident in Colombia involving as many as 20 women and a dozen military personnel appeared to be an isolated one. She said the agency's office of professional responsibility had not received any complaints in the past 2 1/2 years. She said investigators are reviewing earlier time periods as well.

"This behavior was not part of the Secret Service way of doing business," Napolitano testified. "We are going to make sure that standards and training, if they need to be tightened up they are tightened."

The White House said Wednesday that the conduct of the employees punished in the ongoing scandal was "inappropriate" and unacceptable for people representing the United States abroad.

At the hearing, committee chairman Sen. Patrick Leahy, D-Vt., praised the Secret Service as "wise, very professional men and women," and called it shocking that so many of the agency's employees were involved in the scandal.

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"It really was, I think, a huge disappointment to the men and women of the Secret Service to begin with, who uphold very high standards and who feel their own reputations are now besmirched by the actions of a few," Napolitano said.

Sen. Lindsey Graham, R-S.C., pressed Napolitano about whether she believes this was the first incident involving prostitutes and the Secret Service.

"The only reason I suggest that we need to maybe look at little harder is because we're lucky to have found out about this. If there hadn't been an argument between one of the agents and, I guess, a prostitute, for lack of a better word, about money, we'd probably have never known about this."

Napolitano said while she is not aware of a broader culture problem at the Secret Service, Director Mark Sullivan and his investigators are looking into it.

"What the director is doing is reviewing training, supervision, going back and talking to other agents, really trying to ferret out if this is a systemic problem," Napolitano said. "If it is, that would be a surprise to me."

Napolitano also said the government is also reviewing training rules for Secret Service employees to make clear what behavior is acceptable and what's unacceptable.

"The training is focused on professionalism, on conduct consistent with the highest moral values and standards," she said.

Graham told Napolitano that the Secret Service officers and supervisors involved should have known their conduct was wrong: "I don't think it's a lack of training."

Wednesday was the first time Napolitano has faced public questioning from lawmakers since the scandal became public.

The Secret Service announced late Tuesday that all 12 implicated officers had been dealt with: eight forced out, one stripped of his security clearance and three cleared of wrongdoing, all within two weeks of the night in question.

Napolitano pointed to that swift action as evidence that incident is being taken seriously.

"We will not allow the actions of a few to tarnish the proud legacy of the Secret Service," Napolitano said.

She said the Homeland Security inspector general is also supervising the investigation and using "the investigatory resources of the Secret Service." She added add that she expected the inspector general to do a complete investigation.

The scandal erupted after a fight over payment between a Colombian prostitute and a Secret Service employee spilled into the hallway of the Hotel Caribe ahead of President Barack Obama's arrival at the Summit of the Americas in Cartagena. A dozen military personnel have also been implicated, and Defense Secretary Leon Panetta said they have had their security clearances suspended.

Pentagon officials are expected to brief Senate Armed Services Committee Chairman Carl Levin and ranking Republican John McCain, as well as staff members from the House Armed Services Committee Wednesday.

Obama said Tuesday the employees at the center of the scandal were not representative of the agency that protects his family in the glare of public life. "These guys are incredible. They protect me. They protect Michelle. They protect the girls. They protect our officials all around the world," the president said on NBC's "Late Night With Jimmy Fallon."

"A couple of knuckleheads shouldn't detract from what they do," Obama added. "What these guys were thinking, I don't know. That's why they're not there anymore."

Wednesday, presidential spokesman Jay Carney said Obama's opinion on the issue hadn't changed.

"The president said that if the accusations that had surfaced at the time turned out to be true, he would be angry. And of course, he is angry," Carney told reporters traveling with Obama on Air Force One.

Lawmakers across Congress say they are concerned about the security risk posed by the proximity the prostitutes — as many as 20, all foreign nationals — had access to personnel with sensitive information on the president's plans.

"No one wants to see the president's security compromised or America embarrassed," Leahy said.

Napolitano said Wednesday that there was no risk to the president.

Elsewhere on Capitol Hill Wednesday, House Speaker John Boehner said the scandal is an embarrassment to the agency and the United States, but stopped short of calling for an independent investigation.

"What I'm looking for are the facts. I don't want to just jump out there and make noise just to be making noise," Boehner told reporters. "Let's get to the bottom of this."

The Colombia scandal has been widely denounced by official Washington, but it's a delicate political matter in an election year with the presidency and congressional majorities at stake. All sides have praised Sullivan's swift action and thorough investigation, in part because he's spent significant time keeping key lawmakers in the loop.

In a similar but unrelated incident, Panetta said Tuesday that three Marines on a U.S. Embassy security team and one embassy staff member were punished for allegedly pushing a prostitute out of a car in Brasilia, Brazil, last year after a dispute over payment. Panetta, speaking in Brasilia, said he had "no tolerance for that kind of conduct."

Another Senate panel is looking for a pattern of misconduct. Sen. Joe Lieberman, chairman of the Homeland Security and Governmental Affairs Committee, told reporters on Tuesday that he'll hold hearings on the service's culture and whether clear rules exist on how employees should behave when they are off duty but on assignment.

"I want to ask questions about whether there is any other evidence of misconduct by Secret Service agents in the last five or 10 years," Lieberman said. "If so, what was done about it, could something have been done to have prevented what happened in Cartagena? And now that it has happened, what do they intend to do?"

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Associated Press Writers Alicia A. Caldwell, Julie Pace, Ben Feller, Jim Kuhnhenn and Donna Cassata in Washington and Lolita C. Baldor in Brasilia, Brazil, contributed to this report.