Mr. Strauss-Kahn, 62, who was widely expected to become the Socialist candidate for the French presidency, was apprehended by detectives of the Port Authority of New York and New Jersey in the first class section of the jetliner, and immediately turned over to detectives from the Midtown South Precinct, which covers the part of Manhattan where the hotel is, officials said.

“He is in N.Y.P.D. custody, being questioned in connection with sexual assault of a hotel chambermaid earlier this afternoon,” Deputy Commissioner Paul J. Browne, the New York Police Department’s chief spokesman, said Saturday evening.

A spokeswoman for the office of the Manhattan district attorney said that Mr. Strauss-Kahn had not yet been, “formally charged,” in the case, and that he was not expected to be arraigned before a judge until later in the evening.

The apprehension came at about 4:40 p.m., when two detectives of the Port Authority of New York and New Jersey suddenly boarded Air France Flight 23, as the plane idled on the tarmac, said John P. L. Kelly, a spokesman for the agency.

“It was 10 minutes before its scheduled departure,” said Mr. Kelly. “They were just about to close the doors.” Mr. Kelly said Mr. Strauss-Kahn was traveling alone and was not handcuffed during the apprehension.

“He complied with the detectives’ directions,” Mr. Kelly said.

The Port Authority officers were acting on information from the Police Department, whose detectives had been investigating the assault of a female employee of the Sofitel New York, at 45 West 44th Street, in the heart of the theater district.

Mr. Strauss-Khan, a former French finance minister, had been expected to declare his candidacy soon after three and a half years as the leader of the fund, which is based in Washington, where he was considered by many to have done a good job in a very difficult period of global economic strain, when the bank itself has become vital to the smooth running of the world and the European economy.

His time at the bank was tarnished in 2008 by an affair with a Hungarian economist who was a subordinate there.

The fund decided to stand by him despite concluding that he had shown poor judgment in conducting the affair.

Mr. Strauss-Kahn issued an apology to employees at the bank and his wife, Anne Sinclair, an American-born French television journalist.

In his statement then, Mr. Strauss-Kahn said, “I am grateful that the board has confirmed that there was no abuse of authority on my part, but I accept that this incident represents a serious error of judgment.”

The economist, Piroska Nagy, left the fund as part of a buyout of nearly 600 employees instituted by Mr. Strauss-Kahn to cut costs.

In the New York case, Mr. Browne said that it was about 1 p.m. on Saturday when the chambermaid, a 32-year-old woman, entered to clean Mr. Strauss-Kahn’s room.

“He came out of the bathroom, fully naked and attempted to sexually assault her,” Mr. Browne said.

( Source: The New York Times )