High-level officials at NASA concurred with the engineering report, which was issued on Day 12 of the doomed 16-day flight, the officials said.

Today, 48 hours after the disaster, NASA's top spaceflight official, William Readdy, said the damage done by the broken-off piece of fuel-tank insulation is now being looked at very carefully as a possible cause of the tragedy.

"Although that may, in fact, wind up being the cause ­ it may certainly be the leading candidate right now ­ we have to go through all the evidence and then rule things out very methodically in order to arrive at the cause," he said.

The shuttle broke up 39 miles over Texas and fell to Earth just as it was experiencing maximum re-entry heat of 3,000 degrees. All seven astronauts aboard perished.

Columbia was covered with more than 20,000 thermal tiles to protect it from burning up while re-entering Earth's atmosphere. During liftoff Jan. 16, a hard piece of foam insulation hit the spacecraft's left wing 80 seconds after launch.

That led NASA engineers to conduct thermal analyses and a frame-by-frame examination of the launch footage.

Ron Dittemore, the shuttle program manager, said today that photos showed the piece of insulation was about 16-by-6-by-20 inches in size and weighed about 2.67 pounds, and could have smashed into the thermal tiles on the underside of the left wing area.

Analyses were performed for different scenarios, including different weights for the debris and the possibility of tile damage over an area of about 7 inches by 32 inches, NASA said.

The engineering report cited by Readdy indicated "the potential for a large damage area to the tile." But it went on to note that the damage should be limited to the coating on the tiles and have no effect on the mission.

"These thermal analyses indicate possible localized structural damage but no burn-through and no safety-of-flight issue," the report concluded.

"We were in complete concurrence," Michael Kostelnik, a NASA spaceflight office deputy, said at a news conference today with Readdy.

Readdy said he also was part of the discussions held throughout the flight on the matter.

"The best and brightest engineers we have who helped design and build this system looked carefully at all the analysis and the information we had at this time, and made a determination this was not a safety-of-flight issue," Kostelnik said.

Columbia broke up just 16 minutes from its scheduled landing in Cape Canaveral, Fla. NASA said temperature data showed that the left side ­ the same side hit by the debris ­ heated up sharply just before the shuttle disintegrated.