A piece of wreckage from the space shuttle Columbia found last week in Texas is from the spaceship's left wing, possibly offering a crucial piece of evidence in the hunt for the cause of the disaster, officials said yesterday.

Investigators identified the two-foot-long section as being from the front edge of the left wing, which may have suffered damage during liftoff that caused the shuttle to rip apart during reentry 16 days later.

Engineers searching for clues to the shuttle's destruction were examining the section of debris at Barksdale Air Force Base outside Shreveport, La., where it was taken after being found near Lufkin, Tex., on Friday.

"I don't know exactly what section that is along the wing. And there wasn't certainty among the people who had recovered it," Michael Kostelnik, the space agency's deputy associate administrator, said at a briefing at NASA headquarters.

Investigators are looking at a variety of factors as possible causes of the Columbia's disintegration over Texas on Feb. 1, including whether the leading edge of the shuttle's left wing was damaged, allowing it to burn during the 3,000-degree heat of reentry into Earth's atmosphere. A Boeing analysis of the Columbia's flight has said that if a piece of ice had been shed from the shuttle's external fuel tank at the high speeds of liftoff, it could have penetrated the super-hard coating on the wing's edge. Space debris also could have struck the shuttle.

Thousands of pieces of the shuttle have been collected by searchers in east Texas and taken to Barksdale and another nearby military base. Eventually, the pieces will be transported to Cape Canaveral, where NASA engineers hope to reassemble the spacecraft.

Because sensors showed that the left wing was dragging and the shuttle was struggling to compensate for it in the final minutes of flight, NASA engineers have been especially interested in learning more about what happened to the wing.

The section that was found is coated with a dense material known as reinforced carbon-carbon, which is designed to provide the best protection against the most intense heat that space shuttles encounter during reentry. The section may also have some protective ceramic tiles attached to it, which could enable investigators to determine its exact location on the wing because every tile is marked with an identifying serial number, Kostelnik said.

Investigators are continuing to search for pieces of the left wing because it was struck by a chunk of foam insulation that broke off the shuttle's external tank during liftoff. The impact may have damaged the ship's protective shell, leaving Columbia's aluminum skin vulnerable at reentry.

Yesterday, divers and a Coast Guard underwater rover examined three objects deep in the murky waters of the Toledo Bend Reservoir in east Texas that they said could be large pieces of the shuttle. One 40-pound piece of metal about 21/2 feet in diameter and a foot thick was pulled up, but officials said they did not know if it came from Columbia. Search crews have been concentrating on a two-mile-wide swath of pine groves and swamps that cuts about 35 miles through rural Sabine County.

The relatively narrow strip of east Texas land and water is where NASA officials believe the bulk of Columbia's debris fell, and search crews were looking in areas between the tiny towns of Bronson and Hemphill, where they believe important components are obscured in the briars. In Nacogdoches County, a farmer found what appeared to be gauges in a field, authorities said.

Searchers here have already covered 11,000 acres of terrain, finding hundreds of debris sites and thousands of pieces of the shuttle.

"This is an enormous jigsaw puzzle," said one of the searchers, Army National Guard Lt. Adam Collett. "They need us to help them put it back together, and we're taking great care to provide the best information we can."

Blue skies and warming temperatures provided the best search conditions in almost a week, breaking the steady, cold rains that have drenched the area and have complicated the massive effort. Searchers and local authorities said the bright sun was making an immediate impact, as crews were discovering many more items.

"The sun is shining, things are warming up, and we're all on cloud nine," said Sabine County Sheriff Tom Maddox. "We're doing extremely well, and we're making significant finds . . . including an array of shuttle material and human remains."

Maddox said the materials are too massive to quantify, and run the gamut from tiny scraps to large pieces such as doors, windows and chunks of the shuttle's superstructure. Crews were able to reach some remote and thickly covered forest areas in yesterday's sunlight, slogging through the waterlogged brush.

"It's been a nightmare covering all that needs to be covered," Maddox said. "The sheer magnitude of it is just staggering. But our spirits are high. We're more determined than ever."

Authorities are equally determined to find pieces that were picked up by people living in the region and that were not turned in to federal officials.

Yesterday, the Associated Press reported that Harrison County Constable Robert Hagan II, 45, was charged by federal prosecutors with theft of government property for taking a piece of tile and other debris while assisting in the search on Feb. 1 and 2 near Nacogdoches. Hagan is the third person charged with looting shuttle debris.

White reported from Hemphill, Tex.

Employees of NASA contractor United Space Alliance and members of the investigation team unpack and examine a window assembly from the space shuttle Columbia yesterday at Barksdale Air Force Base in Louisiana.Grid marks are placed inside a hangar at Kennedy Space Center yesterday to prepare for the possible reconstruction of the space shuttle Columbia.