HOUSTON, Texas, February 4 (News agencies) – The U.S. space agency NASA is investigating whether a stray piece of insulation doomed the space shuttle Columbia by damaging its heat shield, officials said as they extended their search for debris and crew remains to the western United States.

Engineers had concluded after an exhaustive analysis that the piece of foam which broke off the shuttle's external fuel tank during the January 16 launch and struck the left wing did not pose a safety threat.

However, National Aeronautics and Space Administration (NASA) officials admitted on Monday, February 4, that the engineers' conclusion may have been wrong and investigators are now focusing on the foam as the leading suspect in causing the problem that broke up the Columbia over the southern United States as it re-entered the Earth's atmosphere, killing all of the seven astronauts aboard.

"This debris is one of our primary areas of emphasis. We are completely redoing our analysis from scratch," shuttle program manager Ron Dittemore was quoted by Agence France-Presse (AFP) as saying.

"We're making the assumption that the external tank was the root cause of the problem that lost Columbia” Dittemore added.

"Even though that's a drastic assumption that's what I think we need to do."

NASA analysts considered the possibility the impact from the piece of foam, which weighed slightly more than a kilogram, might damage one or more of the ceramic tiles which form the shuttle's heat shield, Dittemore said.

However, they did not expect the damage to be severe enough to threaten the shuttle on re-entry, when temperatures reach 1,650 degrees Celsius (3,000 degrees Fahrenheit), he said.

Pieces of insulation had broken off on previous shuttle missions and impacted the spacecraft, but caused no significant damage, he said.

Dittemore said investigators remain baffled after two days of analyzing data as to why temperatures on Columbia's left side spiked as much as 16 degrees Celsius (60 degrees Fahrenheit) in the minutes before contact was lost with the spacecraft about the time an unusual amount of drag caused the shuttle to roll to the left.

Prompted by what has already been learned, the agency has assembled a special team to search for debris west of the parts of Texas and Louisiana where most of Columbia's remains have been found, he said.

Such debris could be significant because it could provide the vital missing link to the disaster, Dittemore said.

"We are extremely interested in any debris upstream of the primary impact area," he said.

Investigators also were talking to an amateur astronomer who said he had seen pieces of the shuttle break off as it crossed over California, where the first indications of a problem are now known to have surfaced, he said.

Meanwhile, hundreds of other investigators and volunteers hunting for the wreckage of Columbia fanned out over a 200-mile (320-kilometer) zone in eastern Texas and Louisiana in helicopters, on horseback or on foot in sticky mud.

The shuttle's nose cone was located late Monday buried in the ground near the Texas-Louisiana border, Fox News reported, quoting officials as saying they would try Tuesday to excavate it.

"We were just told that it was in fairly good condition," Sabine County, Texas, Sheriff Tom Maddox told Fox.

Authorities have repeatedly warned the public not to touch any fragments, which may be covered with toxic propellants.

The grim search already has uncovered numerous remains from the astronauts including a torso, a leg, a skull and even a finger with a ring on it.

The remains are being tagged and transported by plane and truck to Barksdale Air Force Base in Louisiana, where a panel of outside experts appointed by NASA met to look into the disaster.

The investigation of the disaster has revived longstanding concerns about safety in the US space program. Leaders in both the US Senate and House of Representatives said they will hold hearings on the issue.

Space Budget Increase  

In another related development, the Bush administration proposed a 3.1-percent increase of its space budget, which highlights search for extraterrestrial life but puts on hold a new generation of manned orbiters.

The spending blueprint, unveiled by the White House Monday, requests nearly 15.5 billion dollars for NASA in fiscal 2004 beginning on October 1, up from 15 billion dollars NASA is projected to spend in the current fiscal year.

It also mysteriously hints that "perhaps the notion that 'there’s something out there' is closer to reality than we have imagined" -- and generously provides for unmanned exploration of the far reaches of outer space in search of past or existing life.

But it leaves unanswered the question how Columbia's fiery demise last Saturday will affect future spending on the space program.

"This administration is making no conclusions about whether the funding over the last decade or the increase in funding has anything to do with what took place on the Columbia," White House spokesman Ari Fleischer told reporters. "It would be premature and unwise to make any judgments about that at this time."

Funding for the space shuttle itself will go up 24 percent -- from 3.2 billion dollars this year to 3.9 billion the next.