WASHINGTON – Senators investigating the Secret Service prostitution scandal said Wednesday that dozens of reported episodes of misconduct by agents point to a culture of carousing in the agency and urged Director Mark Sullivan to get past his insistence that the romp in Cartagena was a one-time mistake.

The disconnect between the senators and Sullivan reappeared again and again throughout the two-hour hearing, even as the Secret Service chief for the first time apologized for the incident that tarnished the elite presidential protection force. By the end, Sullivan’s job appeared secure even as new details emerged that left little doubt, senators said, that a pattern of sexual misbehavior had taken root in the agency.

“He kept saying over and over again that he basically does think this was an isolated incident, and I don’t think he has any basis for that conclusion,” said Sen. Susan Collins of Maine, the senior Republican on the Homeland Security panel that heard Sullivan’s first public accounting of the episode.

“For the good of the Secret Service,” added Sen. Joe Lieberman of Connecticut, the panel chairman, “he’s got to assume that what happened in Cartagena was not an isolated incident, or else it will happen again.”

Still, Sullivan insisted repeatedly that in his 29-year Secret Service career, he had never heard anyone say that misconduct was condoned, implicitly or otherwise.

“I just do not think that this is something that is systemic within this organization,” Sullivan said.

He didn’t make much progress on that front, as senators offered fresh evidence of what they considered reckless behavior. Lieberman said 64 allegations or complaints of sexual misconduct were made against Secret Service employees in the last five years.

Three of those, Lieberman said, were complaints of inappropriate relationships with a foreign national and one of “nonconsensual intercourse,” on which he didn’t have enough information to elaborate. Sullivan said that complaint was investigated by outside law enforcement officers, who decided not to prosecute.

Thirty other cases involved alcohol, Lieberman said, almost all relating to driving under the influence.

Sullivan also told the committee an agent was fired in a 2008 Washington prostitution episode, after trying to hire an uncover police officer.

Charles Edwards, the inspector general at the Homeland Security Department conducting his own probe, and Sullivan discussed an episode from the 2002 Olympics when at least three agents were caught in a rowdy, drunken party in the agents’ hotel rooms with college-age women under 21.

They were accused of plying the women with alcohol, and two were accused of but not charged with sexual misconduct. One agent was charged with disorderly conduct. The agents involved left the Secret Service, Edwards and Sullivan said.

Against that backdrop, Colombia was probably not an aberration, lawmakers said.

“It’s just hard to believe that this is just a one-time occurrence,” said Sen. Ron Johnson, R-Wis.

But Sullivan stuck to that reasoning, pointing out that the dozen agents and supervisors implicated in the Colombia incident were a tiny fraction of the agency’s 7,000 employees.

“I can understand how the question could be asked,” Sullivan said, calling his employees “among the most dedicated, hardest-working, self-sacrificing employees within the federal government.”

He also said that Obama’s security was never at risk. The officers implicated in the prostitution scandal could not have inadvertently disclosed sensitive security details because their confidential briefing about Obama’s trip had not taken place.