From the moment the space shuttle Columbia streaked through the fringes of space over California Saturday morning, onboard instruments showed a sharp temperature spike on the orbiter's left side, and by the time it crossed over New Mexico its flight control system was registering the most extreme steering adjustments ever seen in a descending shuttle.

The onboard computer system was apparently trying to correct for something creating drag on the left side of the spacecraft, said shuttle program manager Ron Dittemore at an early evening briefing. The computer was commanding the moveable flaps -- the elevons -- to roll Columbia back to the right.

The new details appeared to paint a picture of a spacecraft that was running into trouble almost as soon as it began its plunge back into Earth's atmosphere after a seemingly flawless 16-day flight.

NASA's accelerating probe of the crash has not yet pinpointed a cause for the unusual readings, Dittemore said, speaking to reporters at NASA's Johnson Space Center in Houston. But one possible source was rough or missing pieces of the shuttle's insulating tile at a crucial spot. Investigators are looking carefully at the possibility that the damage began when a piece of soft insulating foam struck the left wing after shearing away from the shuttle's external tank 80 seconds after liftoff on Jan. 16.

One day after the shocking loss, multiple investigations were getting organized yesterday while "mishap response" teams gathered at Barksdale Air Force Base near Shreveport, La., and in Lufkin, Fort Worth and Dallas, Tex., to help collect information and debris. And in a number of NASA centers, numerous engineering teams were burrowing deeper and deeper into the available data from the flight.

As he disclosed the emerging details of the shuttle's last minutes, Dittemore cautioned that the engineering analysts were still just beginning to assemble the pieces needed to complete the puzzle, and the evidence might seem contradictory from one day to the next. As the analysts delve more deeply into the recorded data, he said, they expect to extract perhaps another half-minute or so of data from the shuttle's final seconds.

Although the potential tile damage has drawn considerable attention, he said, engineers could not rule out other possibilities such as a structural or flight control system failure.

"We've got some more detective work, but we're making progress inch by inch," he said.

The sensor data showed that at 8:53 a.m. Eastern time Saturday, as the shuttle passed over California, temperatures rose 20 to 30 degrees in five minutes inside the shuttle's left wheel well. "This is significant," Dittemore said, because the measurements were taken in a spot particularly vulnerable to heat if the tile shielding is failing. It was the first significant episode of unusual heating in the descent.

At 8:54, over eastern California and western Nevada, areas on the left fuselage around the wing also showed an unusual temperature rise. While the shuttle's right side showed a routine 15-degree rise, the left side warmed 60 degrees. Inside the shuttle's big cargo bay, temperatures were normal.

At 8:58 a.m., over New Mexico, he said, "The roll trim and the elevons started to increase, indicating that we had an increase in drag on the left side of the vehicle. . . . At this time, we also lost the left, main landing gear tire pressure and wheel temperature measurements." The signs were that the tire was still there, but the sensors were somehow ruined.

At 8:59 a.m., over west Texas, there was another increase in drag on the left side, indicated by the flight control system's struggle to counter the drag by commanding the vehicle to roll to the right.

Then the shuttle's radio signal was lost.

NASA yesterday called on the public on the West Coast to provide photos or video of the shuttle as it hurtled overhead. Dittemore said the agency already has statements from several people who thought they saw something separate from the space-plane.

As Dittemore spoke in Houston, accident investigators were converging on key points in Texas and Louisiana, and a partnership of federal and local agencies was attempting to corral the debris of the fallen shuttle -- now vital forensic evidence -- that lay strewn on roofs, in cow pastures and parking lots across the landscape.

A team of independent investigators was due to hold its first meeting today at Barksdale Air Force Base, where a command post has been set up. Some or all of the debris could be collected there.

Retired Navy Adm. Harold W. Gehman Jr., who headed the investigation of the attack on the USS Cole in Yemen in October 2000, will lead the independent investigation, one of several focusing on the shuttle accident. Other members of the panel, announced yesterday by NASA Administrator Sean O'Keefe, include active-duty officers from the Navy and Air Force, an aviation expert from the Department of Transportation and an accident investigator from the Federal Aviation Administration.

Several senior NASA officials will also join the panel, including Bryan D. O'Connor, NASA associate administrator, a former astronaut.

The National Transportation Safety Board has sent six investigators to help with the effort, including two men who worked on the crash of Trans World Airlines Flight 800 -- Robert Benzon and Frank Hilldrup -- and the board's forensics expert, Frank Ciaccio, who normally assists coroners in body-part identification.

Under usual safety board procedures, local authorities are told to move wreckage only when necessary to recover human remains. Otherwise, the wreckage stays in place until an experienced investigator can examine it, photograph it from all angles and document its exact location by Global Positioning Satellite coordinates. Only then is it moved to a central location.

Radar records of the shuttle's thunderous descent will play a major role in documenting the in-flight breakup and the location of wreckage, experts said.

Mike O'Rourke, a radar expert who worked on the investigation of the shuttle Challenger explosion for the safety board and the TWA Flight 800 crash for the FBI, said numerous radar installations and possibly some airborne radar should have recorded the shuttle's descent.

At least six of the FAA's more modern ARSR-4 radars were in position to record the descent once it dropped to between 110,000 and 100,000 feet, he said. In addition, he said, one or more of U.S. Space Command's Aerostat radars would have picked it up. These radars are mounted on tethered balloons at altitudes of 8,000 to 14,500 feet and can look up and down.

The Customs Service also may have recorded radar tracks if any of its P3 radar aircraft were in flight at the time. These aircraft are usually used to look for drug-smuggling planes.

"They're going to have an awful lot of radars," said O'Rourke, now a Northern Virginia consultant.

He said certain sensitive radars can track fragments as small as a yard square. Still, O'Rourke said, it will be very difficult to find some pieces.

"It's going to be hard," he said. "In that area, there are leaves on the ground. Some of this stuff is going to bury itself, especially if the ground is soft."

O'Rourke said that some of the smallest pieces, such as computer chips with "nonvolatile memory," can give investigators data that may not have been relayed to the ground.

NASA officials disclosed yesterday that the external fuel tank that lost a piece of foam at launch was one of the last two remaining of an older "lightweight" model that is significantly heavier than newer "super lightweight" tanks. The older model had flown successfully in almost 90 missions.

The loss of the insulation was noticed during routine review of launch videos the day after the launch, Dittemore said. Although it appeared to strike the left wing of the orbiter, extensive analysis led NASA engineers to conclude at the time that the event was "inconsequential" and unlikely to have caused any damage.

The 154-foot-long tank, built by Lockheed Martin Space Systems, contains liquid propellant for the shuttle's three main engines. The new super-light model weighs about 7,500 pounds less than the older ones.

Lockheed spokesman Harry Wadsworth said he did not believe the insulation would adhere any differently to the older model. The insulation is essentially the same and is sprayed on. The older tanks "have a very good track record."

Staff writer Dan Eggen and researcher Karl Evanzz contributed to this report.

Investigators are considering whether a piece of insulating foam that fell off during Columbia's ascent on Jan. 16 may have damaged the left wing.In this sequence of images taken from video, what appears to be debris (circled in the second and third frames above) is seen striking the underside of the left wing of the space shuttle Columbia during its ascent into space Jan. 16. Investigators are examining whether a piece of soft insulating foam that broke off shortly after liftoff may have damaged the left wing.

At a press briefing in Houston yesterday, shuttle program manager Ron Dittemore discusses Columbia's flight behavior as it approached landing.