Investigators believe that as many as 21 women were brought by U.S. Secret Service and military personnel to the Hotel Caribe in Cartagena, Colombia, last week during a night of carousing, a dramatic increase in the number of women previously disclosed by government officials.

Officials said 11 Secret Service and 10 military personnel are suspected of misconduct that took place before President Obama arrived in Colombia for an economic summit. Initial reports suggested that the military personnel, some of whom were confined to their rooms after the scandal broke, had violated curfew, while the Secret Service members had engaged with the women, who were allegedly working as prostitutes.

But Sen. Susan Collins (R-Maine) said Tuesday that Secret Service Director Mark Sullivan told her that the preliminary investigation has determined that 20 or 21 women were brought to the hotel last Wednesday night. Agency investigators in Cartagena have obtained copies of the women’s identification cards, which they were required to present at the hotel, and are attempting to interview some of the women, said Rep. Peter T. King (R-N.Y.), head of the House Committee on Homeland Security.

King said investigators have determined that none of the women were minors.

In a statement, Secret Service spokesman Ed Donovan said that Sullivan briefed Collins on the investigation “and advised her that 21 U.S. personnel were involved, to include 11 Secret Service personnel. The allegations involved misconduct with women. The exact number of individuals beyond the U.S. personnel is still under investigation.”

The disclosures make clear that what first appeared to be an isolated case of misbehavior was in fact a night of more widespread debauchery that included heavy drinking and a trip to the Pleyclub, a strip club where the men allegedly paid for women’s services. The participation of two Secret Service supervisors, according to people with knowledge of the investigation, suggests that the men had little fear of repercussions — until hotel workers and Colombian police reported the matter to the U.S. Embassy.

At his daily briefing, White House press secretary Jay Carney said Obama has “confidence” in Sullivan’s leadership of the Secret Service and is awaiting the results of an internal investigation.

“Sullivan acted quickly in response to this incident, and he’s overseeing an investigation as we speak,” Carney said. “This incident needs to be investigated, and it is being investigated. We need to see what the investigation reveals. We’re not going to speculate about the conclusions it might reach.”

Collins, the ranking Republican on the Senate Homeland Security and Governmental Affairs Committee, said Sullivan told her that “the most important quality for a Secret Service officer is character. If the facts prove to be as reported on this, this is an incredible lack of character and breach of security, and potentially extremely serious.”

The Secret Service has revoked the top-secret security clearances of the 11 men under investigation and placed them on administrative leave. The men have also turned in their agency BlackBerrys, said King, who said the men did not have any sensitive documents in their hotel rooms. He added that some of the men said they did not know that the women were prostitutes.

“Even if they weren’t prostitutes, it’s not right to bring foreigners back to their rooms,” King said. “It would probably be safer if they were prostitutes because then we would know who they were working for.”

Two of the Secret Service personnel are senior agents paid at the higher levels of the government’s pay scale, according to congressional officials with knowledge of the investigation.

The two agents, whom one official referred to as “GS-14s,” are near the top of the General Schedule, the compensation system for federal employees. Depending on where the agents are based and other factors, they could earn $110,000 or more annually. Two people with knowledge of the investigation described the men as supervisors.

Meanwhile, the military is continuing its own investigation of last Wednesday’s incident.

An Air Force colonel and a military lawyer assigned to lead the inquiry arrived in Colombia on Monday, the same day the military personnel involved flew back to Florida. They include two Marine dog-handlers, five Army Special Forces members, two Navy explosive-ordnance experts and one Air Force member, an official said.

The personnel have since returned to their home bases, and investigators will contact them by phone or in person, according to Col. Scott Malcom, a spokesman for the U.S. Southern Command.

“The investigating officer is keenly aware of the high level of interest in this case and the concomitant need for speed,” Malcom said in an e-mail. “However, he also is instructed to conduct a fair, thorough and complete investigation.”

The military will not set a deadline to finish the inquiry, which will provide recommendations to top commanders on how to proceed, Malcom said.

Prostitution is legal and regulated in Colombia. But U.S. government agencies have varying restrictions governing the solicitation of prostitutes.

The State Department, which aims to eliminate human trafficking, specifically forbids all Foreign Service employees and contractors from engaging prostitutes, even in countries where it is legal.

In June 2008, the agency sent a cable reminding its workers that “irrespective of whether prostitution is legal in the host country, employees should not in any way abet sex trafficking or solicit people in prostitution. DOS employees who engage in this conduct are subject to discipline.”

The rules at the Department of Homeland Security, which oversees the Secret Service, are more vague. According to the regulations, employees are prohibited from engaging in any “criminal, infamous, dishonest, immoral, or notoriously disgraceful conduct, or other conduct prejudicial to the government,” an official said.

A military spokesman said soliciting a prostitute could result in a year of confinement, dishonorable discharge, and loss of pay and benefits.

Sen. Joseph I. Lieberman (I-Conn.), chairman of the Homeland Security and Governmental Affairs Committee, said in a statement Tuesday that the scandal “needs to be thoroughly investigated and, if the allegations are true, people should be punished.”

Staff writer Greg Jaffe contributed to this report.