President Obama speaks with the mayor of Rome, Ignazio Marino, prior to boarding Air Force One at the Fiumicino Airport near Rome.

March 28, 2014 President Obama speaks with the mayor of Rome, Ignazio Marino, prior to boarding Air Force One at the Fiumicino Airport near Rome. Angelo Carconi/European Pressphoto Agency

President Obama will meet with European Union and NATO officials in his first visit to Brussels, the bureaucratic heart of post-Cold War Europe, which he said this week at The Hague is threatened by Russian President Vladimir Putin’s military turn in Ukraine.

President Obama arrived Monday for a nuclear summit in The Hague, where he also will hold talks with other leaders on how to penalize Russia for its annexation of Crimea from Ukraine.

President Obama arrived Monday for a nuclear summit in The Hague, where he also will hold talks with other leaders on how to penalize Russia for its annexation of Crimea from Ukraine.

Three Secret Service agents responsible for protecting President Obama in Amsterdam this week were sent home and put on administrative leave Sunday after going out for a night of drinking, according to three people familiar with the incident. One of the agents was found drunk and passed out in a hotel hallway, the people said.

The hotel staff alerted the U.S. Embassy in the Netherlands after finding the unconscious agent Sunday morning, a day before Obama arrived in the country, according to two of the people. The embassy then alerted Secret Service managers on the presidential trip, which included the agency’s director, Julia Pierson.

Secret Service spokesman Ed Donovan confirmed Tuesday evening that the agency “did send three employees home for disciplinary reasons” and that they were put on administrative leave pending an investigation. Donovan declined to comment further.

The alleged incident took place in Noordwijk at the Huis Ter Duin Hotel, where the president stayed Monday night, a White House official said Wednesday morning. This is a resort town in the Netherlands about 15 minutes outside The Hague.

According to two people familiar with the Amsterdam incident, the three are members of the Secret Service’s Counter Assault Team, known in the agency as CAT.

The alleged behavior would violate Secret Service rules ­adopted in the wake of a damaging scandal in Cartagena, Colombia, in April 2012, when a dozen agents and officers had been drinking heavily and had brought prostitutes back to their hotel rooms before the president’s arrival for an economic summit.

Under the requirements, anyone on an official trip is forbidden to drink alcohol in the 10 hours leading up to an assignment. As members of the advance team for a presidential trip, the CAT members would have been called to duty sometime Sunday for a classified briefing ahead of the president’s arrival on Monday. Drinking late into the night Saturday evening and Sunday morning would have violated that rule.

Obama landed in the Netherlands on Monday for the start of a high-stakes week-long trip to ­Europe and Saudi Arabia in the midst of a tense standoff with Russia over its annexation of Crimea. The agents involved in the misconduct were among hundreds of U.S. personnel from the Secret Service, the military, the State Department and other agencies sent to prepare for his arrival and ensure his safety, including during his attendance at the Nuclear Security Summit in The Hague with dozens of world leaders.

The president’s visit started with a brief stop at the Rijksmuseum, a fine-arts museum in Amsterdam, with Prime Minister Mark Rutte. Obama traveled from The Hague to Brussels on Tuesday night.

The three involved in the drinking incident were GS-13-level agents, according to one person familiar with the investigation of the case. One of the three was a “team leader” on counter­assault, but he was not in a supervisory position in the agency, the person said.

All three people familiar with the case requested anonymity in order to discuss details of the ongoing investigation. Pierson traveled on Air Force One with Obama, and she is scheduled to remain on the trip with the president as he continues to Rome and Saudi Arabia, one of the people said.

The Counter Assault Team’s job is to protect the president if he or his motorcade comes under attack and to fight off assailants and draw fire while the protective detail removes the president from the area.

Two former agency employees with experience on foreign trips described the counterassault team as one of the most elite units in the agency, responsible for “the last line of defense” for the president. Those selected for CAT are required to be highly skilled shooters and extremely physically fit, with a demanding training regimen, said the two former employees, who spoke on the condition of anonymity to describe internal operations.

There are also high expectations for personal conduct on the squad, they said. On foreign trips, one former agent recalled, the counterassault team often worked shifts as long as 12 hours, the former agents recalled, and agents were expected to get rest during their time off to be in prime condition.

“They received the best technical training in the service,” said one of the former agents. “They were the only team constantly training — training on assaults, on evacuations, all sorts of things. They were very squared away. It was really difficult to get on CAT.”

In the Cartagena scandal, the Secret Service employees’ actions were discovered when one prostitute got into a noisy dispute with agents in a hotel hallway about an agent’s refusal to pay her fee. Colombian police reported the incident to the U.S. Embassy there.

Obama said at the time that the agents’ behavior was unacceptable. “We’re representing the people of the United States, and when we travel to another country I expect us to observe the highest standards, because we’re not just representing ourselves,” he said in Cartagena.

The revelations in Cartagena led to the removal of 10 agents from their jobs, multiple federal and congressional investigations, and the rules aimed at preventing similar activity in the future. Mark Sullivan, the Secret Service director at the time, apologized for his employees’ conduct. Sullivan retired in February 2013 after 30 years in the agency.

Scott Wilson in The Hague contributed to this report.