British scientists said yesterday that a recently rediscovered skeleton first excavated at Stonehenge in the 1920s is that of a man who was decapitated with a single sword stroke to the back of the neck, raising new questions about the mysterious stone formation.

An archaeologist found the skeleton in the British Museum of Natural History, where it was taken after its original storage place at the Royal College of Surgeons was badly damaged by bombs during the London blitz in World War II.

The skeleton, of a 5-foot-5 man about 35 years old, is one of four ever to have been found at Stonehenge, whose fabled circle of prehistoric stone megaliths has been interpreted as everything from a ceremonial site for druids to an ancient astronomical observatory.

The skeleton was excavated by British Lt. Col. William Hawley in 1923, and may date from the Roman period in the first century B.C. or as late as 1000 A.D., when the historical record is detailed enough to have recorded the beheading.

English Heritage, the British government agency responsible for historical preservation, displayed the skeleton yesterday in London. David Miles, Heritage's chief archaeologist, said experts who are studying it with modern radiocarbon techniques should be able to fix the actual date of death within 30 years.

Stonehenge, on the Salisbury Plain of southern England, was built between 3000 B.C. and 1600 B.C. It began as a circular ditch and earthwork with the cremated remains of many people buried both outside the perimeter and inside the circle.

By 2000 B.C., the biggest of the stone megaliths were in place and the skyline surrounding the site was ringed with Bronze Age burial mounds, called barrows. "These are rich, high-status burials of warrior aristocracy, with gold and weapons," Miles said. "They are well outside Stonehenge, but obviously are supposed to be within sight of it."

It is generally accepted that until that time, Stonehenge served as a religious or ceremonial site, but by 1500 B.C. the archaeological record dwindles, suggesting that the area was abandoned. There was little reason to visit a place on a grassy plain "in the middle of nowhere," even in ancient times, Miles explained, except to participate in a formal rite.

The beheading, however, suggests that the site retained significant ceremonial importance hundreds of years later, Miles said. The name Stonehenge derives from the Old English Stanhenges meaning "Stone Gallows."

In all, there have only been four skeletons found inside the circle of Stonehenge. One, of a robust 5-foot-10 man about 25, was recovered in 1978 and dates from 2300 B.C., about the time when the monuments were being constructed. The man had been shot three or four times with arrows and died of his wounds.

Hawley discovered the other three in excavations between 1922 and 1926. He discarded one that he did not consider significant and reburied another one whose grave appeared to have been dug up previously.

The third, unearthed in 1923, was examined cursorily and taken to the Royal College of Surgeons in London, where it stayed on exhibit until 1938, when, in anticipation of war, curators moved it to subbasement shelters along with other valuable artifacts and medical specimens.

About two-thirds of the collection of 60,000 items was destroyed when the college sustained three direct hits during a German bombing raid in 1941. American ambulances removed the remainder--some 19,000 items, including the skeleton--to 17 houses in the countryside.

At some point after the war, the skeleton was returned to the college, while the skull was transferred to the Museum of Natural History. The rest of the skeleton joined the skull in 1955, and archaeologist Mike Pitts found it while doing research on Stonehenge last year.

Miles said the earliest the beheaded man could have been killed was 100 B.C., the beginning of Britain's Iron Age. Before then, the only metal used in swords was bronze, neither sharp or hard enough to decapitate anyone.

The man's neck was severed cleanly at the fourth vertebra, and the exit stroke cut off the tip of his chin. Miles suggested the execution might have occurred during the Roman invasion around 43 A.D. Vespasian, general of the Roman expeditionary force and later Emperor of Rome, had a habit of beheading recalcitrant local chieftains and druids.

Another possibility, Miles said, was that the man died 500 to 600 years later, a loser in intramural wars between England's various kingdoms. Regardless of which tale turns out to be the most likely, "the fact that somebody was executed inside Stonehenge, who might be an important figure, means it continued to be a highly symbolic place," Miles said.

Miles said there was nothing so far to suggest that the beheading might somehow be linked to Arthurian legend. Arthur, a Briton resisting Anglo-Saxon invaders, may have lived between 500-530 A.D., but Miles said that while he believes the story "has a kernel of historical truth," no one will ever be able to link it to the headless skeleton of Stonehenge.

"The guy's never going to jump up and identify himself," Miles said.