Michael Kostelnik, a NASA spaceflight office deputy, said the debris could be wing material, but he cautioned that the space agency has not determined whether it is connected to Columbia at all.

“Debris early in the flight path would be critical because that material would obviously be near the start of the events” that unfolded during the shuttle’s west-to-east trip across the country, Kostelnik said.

At the same time, investigators in Florida studied sea currents in the Atlantic Ocean near the Kennedy Space Center, trying to determine where heat tiles or other parts that might have fallen off Columbia during its launch would have wound up.

The search up to now has been concentrated from central Texas into central Louisiana. A NASA radar map indicates that is the heaviest debris field.

Underscoring the difficulty of sorting out ordinary debris from shuttle wreckage, Arizona officials said one report from Yuma turned out to be burned toast. And Kostelnik said some suspected shuttle debris in Fort Worth had nothing to do with the spacecraft.

“It’s easy to speculate. It’s easy to be confused. There are a lot of things laying around the country,” Kostelnik said.

The discovery on Monday of one of the biggest and most recognizable pieces of Columbia — the nose cone — underscored how hard it is likely to be to find the thousands of much-smaller bits of debris. The nose cone — about 4 feet across — was discovered drilled into the ground in a deep thicket near Hemphill by two men who were scouring their land for debris.

Reaching the spot requires driving down a dirt road and trudging through prickly briar and muddy stream banks. As they went, searchers used orange flags to mark off what appeared to be small pieces of singed straps made from the kind of material used in seat belts.

Hundreds of searchers, some on horseback and four-wheelers, made several discoveries Tuesday, including more human remains, a seat from the shuttle and cylindrical tanks spewing an unknown gas.

In Vernon Parish, La., a woman out walking found fabric bearing a blue Star of David on a silver background, Sheriff Sam Craft said. The object is presumably a patch from the suit of Israeli astronaut Ilan Ramon.

More than 12,000 recovered remnants, many as small as nickels, have created a growing mosaic of evidence that could take months or years to pick through. The primary search area is larger than West Virginia.

Kostelnik also said that larger and denser pieces, including one of the spacecraft’s engines, fell in Louisiana and are being recovered.