An officer of MI5, Britain's national security agency, has resigned after it was discovered that his wife was one of the prostitutes in an alleged orgy in which Max Mosley, president of the International Automobile Federation, was revealed to have taken part in March.

The Sunday Times reported that the MI5 officer left the agency last month. It described the officer as being in his forties and as having served in the military before joining MI5, where he was involved in surveillance operations.

But MI5 denied Saturday that the agency itself, which is responsible for protecting Britain against threats to national security, was involved in setting up a sting against Mosley.

"Any suggestion that the service was involved in setting up Mosley is total nonsense," the Times quotes a senior Whitehall official as saying.

Mosley, the son of Britain's fascist leader of the 1930s, Oswald Mosley, and of Diana Mitford, one of the famous family of writers and socialites, both of whom were close to Hitler, was videotaped having an orgy with five call girls in March.

The video and an accompanying article were published in the News of the World newspaper and on its Web site on March 30.

Mosley, 68, has rejected numerous calls for his resignation from the FIA, which governs world motor sport and acts as an international umbrella organization for the world's national automobile clubs.

Mosley faces a vote of confidence on June 3 and has been fighting in recent days to persuade national club presidents to allow him to continue in the job.

He has explained in recent days that if he loses the job the organization may lose control of Formula One motor racing, the most important and lucrative series organized under the aegis of the FIA.

This week Formula One goes to Monaco for its crown jewel event, the Monaco Grand Prix, and it will be the first race that Mosley will have attended since the sex scandal broke.

He will not represent the FIA, and the royal family of Monaco has made it clear that it does not want him to attend the event in an official capacity. Mosley lives in Monaco.

The London Times article said that Jonathan Evans, director- general of MI5, informed Gordon Brown, the British prime minister, and Jacqui Smith, the home secretary, that the agency was not involved in any sting.

An unnamed MI5 official refused to identify the officer whose wife was involved, but confirmed that he had resigned. "I cannot talk about individual cases," the official said.

According to the story, Mosley said he had been told by a source close to the security services that he had been targeted in a covert investigation of his private life "by a group specializing in such things for reasons and clients as yet unknown."

In a five-hour sex session with the five call girls in an underground "torture chamber" in Chelsea, west London, the Oxford- educated former barrister is alleged to have re-enacted a concentration camp scene in which he played the role of both guard and inmate.

One of the call girls recorded the session on videotape and provided it to the News of the World for payment. The London Times said it was that woman's husband who worked for MI5.