Defense Department radar shows an object or material coming off the shuttle Columbia as it orbited Earth about one day after its Jan. 16 launch from Florida, NASA officials confirmed late today.

This kind of signal could represent a meteoroid impact, but NASA spokesman Kyle Herring, in Houston, emphasized that its true significance is not yet known. "The Department of Defense has provided the report to NASA, and we're assessing it," he said.

Investigators are looking closely at the shuttle's in-flight schedule, he said, to determine whether the debris might have come from something benign, such as a routine dump of wastewater or supplies. Sometimes ice builds up in connection with the water dump, and the object may have been a chunk of this frozen material.

Engineers are also looking at data from instruments aboard the shuttle that might have registered a sudden vibration or another change in in-flight conditions that could have resulted from an impact.

The material appeared to leave the shuttle at a rate of about 5 meters per second, according to a source cited by CBS News.

NASA and defense officials have long been concerned about the hazards of space junk. The U.S. Space Command tracks about 9,000 pieces of man-made debris from defunct spacecraft and the like. However, when encountered at orbital velocities typically about 17,500 mph, a tiny paint chip can leave a gouge.

A report earlier had warned of possible serious damage from a meteoroid impact on the leading edge of a shuttle wing, and such an impact was already on the investigators' list of potential causes of the accident.

Searchers in Texas found a 6-by-8-foot piece of Columbia in the heart of the shuttle's wreckage field today that they believe is the door cover to a wheel well. Several computer components also were found, Nacogdoches County Sheriff Thomas Kerss said tonight.

Federal authorities expanded the search to an additional seven Texas counties, stretching farther west along the Columbia's flight path. The search now covers 54 counties and parishes in Texas and Louisiana, an enormous area that officials believe still holds the key to what happened.

NASA officials hoped to retrieve important computer and electronic components from the piney woods and swamps that line the Louisiana border, and authorities in Hemphill, Tex., said their discoveries of debris continued as crews pushed into remote areas. Officials in Hemphill and Nacogdoches have found more than 2,850 debris sites containing thousands of pieces of the shuttle.

In Washington, Steven B. Wallace, a member of the Columbia Accident Investigation Board that will seek to make sense of the evidence from the debris and many other sources, said the panel has no deadline for completing its investigation.

"There is no timeline," said Wallace, who is accident investigation director of the Federal Aviation Administration, in an interview. "The number one priority is to get it right."

Wallace said the board will hold daily briefings and occasional public hearings, although no schedule has been established. He said that every piece of evidence will be considered, and that nothing will be ruled in or out until the board is certain what caused the disaster.

"We go back to rule one of accident investigation," he said. "Everything is on the table."

While praising the "dedicated, . . . candid" way that NASA has handled the release of information about the accident , Wallace said the board will follow the traditional information policy used in U.S. civil crash investigations. That usually means confirmed information will be released promptly, but spokesmen will avoid speculating or drawing conclusions.

"NASA was candid about what they knew and everything they were sort of thinking," Wallace said. "It did result in the accident being solved in the press every day. You won't see that happen now."

Police in Nacogdoches said they hoped to finish cataloguing and collecting items from more than 2,000 sites by the end of the weekend and will then move into areas where debris has not yet been reported, Kerss said today.

"They have organized search efforts for places NASA believes need to be searched in a timely fashion," Kerss said. NASA engineers arrived in eastern Texas to help local authorities identify objects that are "of extreme importance to NASA."

Holly Morgan, a spokeswoman for the U.S. Forest Service, said efforts in Hemphill have increased because of the volume and large size of the debris field.

"We're making a major push this weekend," Morgan said. "We're finding a lot of debris here."

NASA officials in Hemphill have been waiting to inspect three suspected pieces of debris submerged in the Toledo Bend Reservoir, which spans the Texas-Louisiana border. Divers placed buoys over target sites but were unable to dive because of high winds and waves.

One of the pieces was of particular interest: U.S. Forest Service spotters said they saw an item that appeared longer than 20 feet resting in one of the lake's inlets, where a fisherman reported seeing a large piece of debris splash down. Authorities said it was unlikely that divers would be able to search for the items until Monday, when temperatures are expected to rise into the 60s and the weather is supposed to clear.

"There's definitely something there that doesn't belong," said Marcus Beard, a U.S. Forest Service ranger. "It's frustrating that we haven't been able to get to it."

Sawyer reported from Washington. Staff writer Don Phillips contributed to this report.

Firefighters enter woods near Hemphill, Tex., where the search for shuttle wreckage has intensified.