SAO PAULO, Brazil - Autopsies have revealed fractures in the legs, hips, and arms of Air France disaster victims, injuries that - coupled with the large pieces of wreckage pulled from the Atlantic - strongly suggest the plane broke up in the air, experts said yesterday.

With more than 400 bits of debris recovered, the top French investigator voiced optimism about determining what brought down Flight 447, but he also called the conditions - far from land in deep waters - "one of the worst situations ever known in an accident investigation."

French investigators are beginning to form "an image that is progressively less fuzzy," Paul-Louis Arslanian, who runs the French air accident investigation agency BEA, said at a news conference outside Paris.

A spokesman for Brazilian medical examiners said yesterday that fractures were found in autopsies on an undisclosed number of the 50 bodies recovered so far. The official spoke on the condition that he not be named, because of department rules.

"Typically, if you see intact bodies and multiple fractures - arm, leg, hip fractures - it's a good indicator of a midflight breakup," said Frank Ciacco, a former U.S. National Transportation Safety Board forensic expert. "Especially if you're seeing large pieces of aircraft as well."

The pattern of fractures was first reported by Brazil's O Estado de S. Paulo newspaper, which cited unnamed investigators. It also reported that some victims were found with little or no clothing, and had no signs of burns.

That lack of clothing could be significant, said Jack Casey, an aviation safety consultant in Washington and former accident investigator. "In an in-air breakup like we are supposing here, the clothes are just torn away."

Casey also said multiple fractures were consistent with a midair breakup of the Airbus A330-200, which was cruising at about 34,500 feet, with 228 people aboard, when it went down May 31 en route from Rio de Janeiro to Paris.

"Getting ejected into that kind of windstream is like hitting a brick wall - even if they stay in their seats, it is a crushing effect," Casey said. "Most of them were long dead before they hit the water, would be my guess."

When a jet crashes into water mostly intact - such as the Egypt Air plane that hit the Atlantic after taking off from New York in 1999 - debris and bodies are generally broken into small pieces, Ciacco said. "When you've had impact in the water, there is a lot more fragmentation of the bodies."

Searchers from Brazil, France, the United States, and other countries are methodically scanning the surface and depths of the Atlantic for signs of the plane. Brazilian Air Force Col. Henry Munhoz said several body parts, as well as pieces of the plane and luggage, had been found by the French amphibian ship Mistral. He did not provide further details.

The plane's flight-data and voice recorders are still missing.