LONDON (AP) _ Prince Edward, youngest son of Queen Elizabeth II, resigned from the Royal Marines Monday, breaking with a longstanding family tradition of military service.

A brief Buckingham Palace announcement capped six days of intense speculation about Edward's future - an issue of consuming interest to most Britons, who cherish the royal family as the embodiment of British values.

But the statement said: ''An announcement about his future plans is not expected for some time.''

Newspapers had said the 22-year-old Cambridge University graduate was under family pressure - especially from his father, Prince Philip, an honorary captain general in the Royal Marines - to finish his yearlong officer's training course and uphold the family image of devotion to duty.

But the palace said Edward decided to quit after four months of his nine- year enlistment because ''he does not wish to make the service his long- term career.''

No specific reason was given for Edward's resignation, and the handsome prince, an amateur actor known as the family prankster, made no public statements. The prince drove to an undisclosed destination after a 10-minute talk Monday with Col. Ian Moore, his commanding officer, at his base in western England.

The Sun newspaper said when it broke the story last Wednesday that Edward was quitting because he found the training ''too tough and demanding.''

But Moore told reporters Monday at the marines' commando training center at Lympstone, 140 miles southwest of London, that the prince ''had all the physical ability to complete his training satisfactorily, indeed well.''

Edward, fifth in line to the throne, was the first member of the British royal family to join the marines, signing on in September 1983, but he followed a long tradition of royal service in the military.

His older brothers, Prince Charles and Prince Andrew, joined the Royal Navy, as did their father Prince Philip, uncle Lord Mountbatten, grandfather King George VI and great-grandfather King George V. Andrew flew helicopters in the 1982 Falklands war and is still in the navy.

Asked how the queen and Philip reacted to Edward's resignation, a palace spokeswoman, speaking on condition of anonymity, said: ''I am sure they understand it.''

Edward did a two-week course with the marines before going to Cambridge to study history on a marine-sponsored cadetship. He spent five weeks a year with the force, including a stint in Britain's former Central American colony of Belize, until his graduation last June.

In September, he started commando training - long hikes carrying 70-pound packs, scaling 30-foot walls, plunging through tunnels filled with icy water.

Edward shares a family love of the outdoors but had to give up rugby at Cambridge after injuring his leg. He hurt a knee and ankle in marine training and came out second best in a boxing match with a black eye and bloody nose.

But Moore said: ''He got a very good report out of his initial training. All the indications are that he had a good career ahead of him. He made his decision for very honorable reasons.''

Fellow marines ranked Edward in the top six of his group of 36 officer trainees. His Cambridge friend, Peter Fraser, 22, also quit the program Monday, but the marines denied newspaper reports they had a pact to resign together.

A Royal Marines statement about Edward said: ''We are obviously disappointed he has resigned his commission and we wish him every success in his future career.''

Edward had to endure derisive newspaper cartoons and insinuations about his manliness, but 81 percent of Britons polled last Thursday by the Sunday Express were sympathetic, saying Edward's future was his own affair.

While deciding on a career, Edward can rely on his taxpayer-funded income of $30,000 a year. But he may have to reimburse the marines for the estimated $12,000 to $15,000 they paid him during his university years.

Edward has taught in New Zealand but says teaching isn't for him. He is said to be looking for an intellectually demanding job. Industry, the diplomatic service, or another branch of the armed forces have been suggested.