Space shuttle Columbia disintegrated 39 miles over Texas on Saturday in a meteoric streak that rained smoking debris over hundreds of miles of countryside. All seven astronauts were lost, a tragedy that echoed the Challenger explosion almost exactly 17 years earlier.

The catastrophe occurred in the last 16 minutes of the 16-day mission as the spaceship glided in for a landing in Florida.

''The Columbia is lost,'' said President Bush, after he telephoned the families of the astronauts to console them.

''The same creator who names the stars also knows the names of the seven souls we mourn today,'' Bush said, his eyes glistening. ''The crew of the shuttle Columbia did not return safely to Earth but we can pray they are safely home.''

The cause of the tragedy was not immediately known. An independent commission was appointed to investigate. One potential focus: possible damage to Columbia's protective thermal tiles on the left wing from a flying piece of debris during liftoff. NASA said the first indication of trouble Saturday was the loss of temperature sensors in that wing's hydraulic system.

The spacecraft had just re-entered the atmosphere and had reached the point at which it was subjected to the highest temperatures.

Authorities said there was no indication of terrorism; at 207,135 feet, the shuttle was out of range of any surface-to-air missile, one senior government official said. Security was extraordinarily tight on this mission because Ilan Ramon, Israel's first astronaut, was among the crew members.

Television footage showed a bright light followed by white smoke plumes streaking diagonally across the brilliant, blue sky. Debris appeared to break off into separate balls of light as it continued downward.

''We saw it coming across the sky real bright and shiny and all in one piece. We thought it was the sun shining off an airplane,'' said Doug Ruby, who was driving with his father along a Texas highway, headed for a fishing trip. ''Then it broke up in about six pieces -- they were all balls of fire -- before it went over the tree line.''

Pieces of the spacecraft were found in several east Texas counties and in Louisiana. There was at least one report of human remains recovered -- in Hemphill, Texas, near the Louisiana line, a hospital employee on his way to work reported finding what appeared to be a charred torso, thigh bone and skull on a rural road near what was believed to be other debris.

The Army's 1st Cavalry Division sent a helicopter search-and-rescue task force from Fort Hood, Texas. NASA also asked members of the public to help in its search for debris, but warned people not to touch the pieces because they might be contaminated with toxic propellants.

The shuttle flight was the 113th in the shuttle program's 22 years and the 28th flight for Columbia, NASA oldest shuttle.

The horrific end of shuttle mission STS-107 was a devastating blow to the nation's space program; the Challenger explosion led to a 2 1/2-year moratorium on launches, and Saturday's accident could bring construction of the international space station to a standstill.