Secret Service Director Julia Pierson has demoted the supervisor of one of the agency’s largest divisions and reassigned nearly two dozen members of its staff, part of a broader cleanup effort in the wake of embarrassing drinking incidents on two recent presidential trips, according to three people familiar with the moves.

The agency also has ordered stricter rules on drinking for employees of the division, known as special operations, prohibiting them from drinking alcohol within 12 hours of reporting for duty and 24 hours before the president’s arrival at any trip location.

Five employees of the special operations division were implicated in misconduct ahead of trips by President Obama last month to the Netherlands and South Florida. The division is central to the agency’s efforts to ensure the safety of the president and his family, and it includes agents and officers trained for unique protective roles such as counter-assault, emergency response and rooftop sniper teams.

A Secret Service spokesman confirmed the reassignment of multiple employees in the division but declined to provide details or elaborate on why they were moved. The spokesman also declined to discuss the removal of Dan Donahue as the special agent in charge of the division.

“Personnel are being reassigned as a result of staffing rotations and as a result of assessments made after two recent incidents of misconduct,” agency spokesman Ed Donovan said. “Director Pierson maintains a zero-tolerance policy regarding incidents of misconduct and continues to evaluate the best human-capital practices and policies for the workforce.”

Donahue ordered the tougher drinking rules after news coverage of alcohol-fueled incidents involving his employees in the Florida Keys and the Netherlands last month, according to an official familiar with the change. Starting Tuesday, Mike Rolin, the former deputy supervisor overseeing the Secret Service’s Washington field office, took over the special operations division, the official and another person briefed on the move said.

Both men declined requests for comment or interviews through the Secret Service.

The beleaguered agency has been struggling for two years to recover from a high-profile drinking-and-prostitution scandal ahead of Obama’s visit to Cartagena, Colombia, for a regional summit in April 2012. The latest incidents have brought fresh embarrassment to the service and harsh new questions for Pierson on Capitol Hill.

Sen. Ronald H. Johnson (Wis.), the ranking Republican on the Homeland Security and Governmental Affairs investigative subcommittee, said in an interview Tuesday that he remains concerned about the Secret Service’s problems and whether the new rules will end them. Agency policy clearly does not allow agents to hire prostitutes and abuse alcohol, he said, yet such incidents have happened multiple times.

“While these rules are a step in the right direction, the real question is how often does this type of misconduct occur, and who is held accountable when it is reported?” Johnson said. “The examples we have from Cartagena, Miami and Amsterdam all involve a third party recognizing and reporting misconduct by USSS employees — not self-

reporting within the agency. An accurate assessment of how prevalent this conduct is within the USSS is long overdue.”

Johnson said he hopes to work with Pierson and the Department of Homeland Security’s new inspector general, John Roth, on an assessment.

In the Netherlands, three Secret Service agents responsible for protecting Obama on a trip to a nuclear summit there March 24 were sent home after going out for a night of drinking the Saturday before. One agent had been found passed out in the hallway of his hotel Sunday morning, where Obama was scheduled to arrive the next day. All three were put on administrative leave based on supervisors’ conclusion that they had violated agency-wide rules that prohibited drinking within 10 hours of reporting for their shifts.

Pierson was about to celebrate her first year on the job as director and learned of the incident while traveling with Obama and other administration officials on Air Force One en route to Amsterdam. The alcohol policies in place at the time had been enacted in the wake of the Cartagena scandal.

Pierson had warned supervisors ahead of the overseas trip that she was already unhappy about another incident of misconduct in South Florida in early March, when two counter-sniper officers suspected of drinking had a car accident just before the first family’s arrival in the area.

In Islamorada, Fla., the two officers were leaving a convenience store in their rented Dodge Caravan at 1:20 a.m. March 7 when the vehicle was hit by an oncoming tractor-trailer. A Florida Highway Patrol trooper said in his report that he smelled alcohol on the minivan driver’s breath and gave the Secret Service officer a field sobriety test. The trooper concluded that the driver was not impaired and did not administer a blood-alcohol test, but he gave him a ticket for causing the accident, the report shows.

Pierson met privately with members of Congress on April 1 and tried to assure them that she found the recent incidents embarrassing and deeply concerning, and she vowed to take immediate steps to fix the problem.

Sen. Thomas R. Carper (D-Del.), chairman of the Senate Homeland Security and Governmental Affairs Committee, said he is confident that Pierson is trying to root out the cause of recurring incidents.

“Unfortunately, troubling incidents like those that occurred recently in the Netherlands and Miami have raised questions regarding the culture of the Secret Service,” Carper said. “While the agency has already enacted a number of reforms, there is still some work to do. I am confident that Director Pierson will take whatever additional steps are necessary to prevent similar incidents of misconduct.”

The special operations division is not the only part of the Secret Service with a history of misconduct problems. The presidential protective detail — the most elite agency team — was stung by revelations this summer that two of its supervisors had engaged in sexually charged

e-mail communications with a female subordinate.

The discovery came after the more-senior supervisor left a government-issued bullet behind in a female guest’s room at the Hay-Adams hotel. He created a scene when he insisted on being allowed to return to the woman’s room to retrieve the bullet and she did not want to let him back in.

Julie A. Tate contributed to this report.