Four Secret Service employees have decided to fight their dismissals for engaging in inappropriate conduct in Colombia last month, a development that could unravel what has been a swift and tidy resolution to an embarrassing scandal over agents’ hiring of prostitutes.

The agents are arguing that the agency is making them scapegoats for behavior that the Secret Service has long tolerated, a charge that Director Mark Sullivan may have to address when he appears before a Senate committee Wednesday. He has not spoken in public about the controversy, but according to his prepared testimony, he plans to tell Congress that there was no breach of operational security.

Several of the implicated agents have told associates that the facts of what happened in Cartagena differ from initial media accounts describing a group outing of a dozen men in search of prostitutes. Instead, the men went to different bars and clubs and met women under a variety of circumstances, in some cases resulting in voluntary trysts that did not involve money.

One 29-year-old field agent assigned to the Washington office, who is single and who resigned under the threat of being fired, told investigators in a polygraph examination that he did not think at the time that the two women he brought back to his hotel room were prostitutes. He is among those seeking to overturn their dismissals, according to three people familiar with his case.

The scandal has badly damaged the Secret Service’s reputation, and the fallout has spread to other federal agencies. A dozen members of the military also are accused of hiring prostitutes on the trip, and the Drug Enforcement Administration is looking into allegations, made by a Secret Service agent during the investigation, that DEA members had previously brought prostitutes to their apartments in Cartagena.

According to interviews with multiple former and current employees and people briefed on the inquiry, the Secret Service agents involved brought women to their hotel rooms without hesi­ta­tion. The agency says it was clear that employees should not do anything unbecoming of a Secret Service employee. Current and former agency employees say sexual encounters during official travel had been condoned under an unwritten code that allows what happens on the road to stay there.

They also contend that this tolerance is part of the “Secret Circus” — a mocking nickname that some employees use to describe what ensues when large numbers of agents and officers arrive in a city.

Shortly after landing in Cartagena at 11 a.m. on Wednesday, April 11, the 55 or so Secret Service members had down time to explore the Caribbean resort. They were there to provide extra security for Obama’s visit for an international summit but had two days before the commander in chief arrived. In Cartagena, prostitution is legal in designated “tolerance zones.”

Secret Service supervisor David Chaney, 48, had spent two decades with the agency and was among the most senior on the plane. He headed out that night to a strip club called the Pley Club, with junior agents in tow, according to two people with knowledge of the events.

Colleagues describe Chaney as gregarious — quick with a joke and to rally for colleagues facing a crisis — and too eager to befriend his subordinates. Efforts to reach Chaney were unsuccessful. Larry Berger, Chaney’s attorney, declined to discuss the details of the case, but said his client put the mission first and never compromised the president’s security.

Chaney has been married for 20 years, but that night he and his colleagues paid the Pley Club a small fee to take at least two of the performers back to the Hotel Caribe, where they and other members of Obama’s advance team were staying, according to the two people familiar with what happened that night.

Separately, a pair of married Secret Service agents who worked together on the agency’s tight-knit, elite counter­assault team — Arthur Huntington and Joe Bongino — headed to the historic old city of Cartagena. They hit the Hard Rock Cafe, which had been recommended in the briefing guide prepared by the State Department, but it was dead. They moved down the street to Tu Candela, a popular bar and disco.

Although the service warns agents in training seminars that extramarital affairs could expose them to blackmail, some married agents are widely known to cheat on their wives. Associates said Huntington, 41, was one who acted differently on many of his trips than he did at home.

Efforts to reach Bongino and Huntington, who has since moved with his wife and two young sons out of their Severna Park home, were unsuccessful.

Huntington’s family has been active in Granite Baptist Church in Glen Burnie.

In Cartagena, while at Tu Candela that Wednesday night, Huntington asked Dania Suarez, a 24-year-old prostitute, to spend the night with him. She agreed in exchange for a “gift” of $800, she later told a television interviewer. Her girlfriend agreed to join Bongino for no charge, Suarez said. People briefed on the investigation corroborated this version of events.

A total of 12 agents were implicated in the activities of that night, after registering the women at the Hotel Caribe’s front desk in keeping with the hotel’s policy for non-paying overnight guests, according to multiple people briefed on the investigation.

Three of those implicated, including Bongino, were cleared of serious misconduct charges. In addition to the four who are challenging their dismissals, at least four others were forced out: Chaney, who immediately took early retirement; Huntington, who was pushed to resign; and two others, who were also dismissed. The fate of one agent is unknown.

One of those cleared is a single agent who speaks Spanish, and who picked up a local woman at the same bar and took her back to his hotel independent of his colleagues, according to two people briefed on the incident. He — along with Bongino and another colleague — kept their jobs after proving that they did not pay for sex. But both the Spanish-speaking agent and Bongino have been shifted off the elite counter­assault team, those briefed on the incident said.

One of those who resigned under pressure but now wants to reverse that move is the single 29-year-old from the Washington field office, who was out with a divorced co-worker from the same office that night. They asked their server at dinner to recommend a non-touristy place for drinks, according to three individuals briefed on the inquiry.

They were directed to a bar with an Egyptian theme, a deejay and a dance floor. Both men later took women from the bar back to their hotel. The divorced colleague has been cleared in the incident, insisting that he told his guest to leave when she asked for money, although he faces minor administrative action.

The 29-year-old agent has told investigators a similar story: that he took two women to his room without realizing they were prostitutes. He maintained, under a polygraph exam, that he told the women to leave when they asked for money for sex, according to associates familiar with his account. He has withdrawn his resignation.

The Washington Post is not naming three of the agents who are fighting their ousters because their cases have not been resolved. Agency supervisor Greg Stokes, another employee recommended for termination and now pushing back against his punishment, has been named in previous reports.

One of those contesting his treatment was not originally under suspicion. That agent took a woman to a different hotel on another night and later came forward voluntarily to inform his bosses that he, too, had a sexual encounter.

The ramifications for that agent have been severe: His pregnant wife threatened to move out, his colleagues said. Like his peers, he was pressured to resign. He hired an attorney to determine whether he can fight for his job.

The morning after the carousing, the party ended for all when Huntington refused to pay Suarez and, she said, pushed her out of his room into the seventh-floor hallway, setting off the dispute that would lead to the exposure of the misconduct.

What none of the agents realized was the extent to which the Secret Service already had irritated the hotel manager, even before the hallway disturbance. The manager, according to people familiar with the investigation, was infuriated by the noise the agents made at the hotel bar and the inconvenience they caused other guests.

Outside the Hotel Caribe, Secret Service officers had repeatedly allowed their bomb-sniffing Belgian Malinois shepherds to defecate on the lone grassy patch along the hotel’s beachfront property — directly in front of the hotel manager’s apartment. The manager did not respond to e-mails and phone messages seeking comment.

After Colombian police alerted the U.S. Embassy, a Secret Service official dispatched to the hotel to investigate found the manager waiting with a clipboard full of complaints and quick to provide names.

On the afternoon of April 12, Paula Reid, the special agent in charge of Miami and South America, conducted initial interviews with the 12 men in Cartagena. Sullivan later ordered all 12 flown home the following morning, just hours before Obama arrived.

But their accounts varied — much more widely than initially reported. Agency investigators concluded that nine of the 12 men paid or solicited prostitutes, but the agents now disputing the findings insist that the punishment outweighs their crimes.

One of the implicated men has told associates that a senior security supervisor had advised agents to follow loose guidelines when spending time with women they met on the road: One-night stands were permitted, this supervisor explained, as long as the relationships were cut off when the agents left the country.

Now, the agency is underscoring off-duty conduct more clearly.

“You should always assume you are being watched when on an official assignment,” a director responsible for the counterassault team warned in a memo to staff members last week. “Do not put yourself in a situation in your personal or professional life that would cause embarrassment to you, your family, or the Secret Service.”

The agency’s rush to judgment came as a shock to the Spanish-speaker, who asked his overnight guest to write a note to his superiors that he thought would clear his name.

“I voluntarily spent the night,” this woman wrote, according to a document reviewed by The Post. “He only gave me $12 to pay for my taxi. . . . It was a pleasure meeting [him] and before saying goodbye I gave him my e-mail address hoping to see him again.”

Only one agent was completely cleared, after proving that someone else had improperly used his name to register a female guest.

Staff writers Carlos Lozada and Joe Davidson and research editor Alice Crites contributed to this report.