NASA today released photographs and videotape that reveal an unusual puff of black smoke coming from the side of space shuttle Challenger's right solid rocket booster less than a second after ignition.

It was the first clear indication that the right booster, the prime suspect in the investigation of the Jan. 28 explosion that destroyed the space shuttle and killed its seven astronauts, malfunctioned at the very start of the launch, when the pressure on the vehicle is greatest.

The National Aeronautics and Space Administration has known for at least three years that a failure was possible at just this moment, according to documents released Wednesday by the agency.

Footage released earlier had suggested that the trouble began about 58 seconds after liftoff, when a fiery plume could be seen on the side of the booster rocket.

In a normal launch, no smoke comes from the side of the booster. While it is not clear from the new pictures exactly where the smoke originated, it appears near the joint between two booster segments that has become a major focus of the inquiry. The unusual smoke identified today appeared dark, in contrast to the normal white smoke that is seen emerging from the rocket's nozzle.

Current and former space agency officials said the puff appears to support a theory that the mechanism used to seal the solid rocket booster segments allowed gas to leak.

Gary Flandro, a solid rocket specialist at the Georgia Institute of Technology, said that because the smoke was dark it probably was not the result of burning fuel but of burning O-ring seals or putty used to help seal the joints. He speculated that if the O-rings failed to seal because they were stiffened by cold temperatures, hot rocket gases could have burned them.

"This could be the start of the whole chain of events" that led to the explosion 73 seconds into the flight, Flandro said.

"This is an extremely significant set of pictures, or we would not have released them," said Hugh Harris, a NASA spokesman.

"This suggests there was a major problem from the start," said Jim Mizell, a retired NASA engineer who has been acting as an agency spokesman since the explosion. "But, again, it is only another part of the story, and we can't say what went wrong until we have all the answers."

Engineers from booster manufacturer Morton Thiokol warned NASA last year that in the first second after ignition the casing and its seals sustain a rapid pressure pulse that can destroy the ability of the backup O-ring to protect against a burn-through if the primary O-ring is burned away by hot gases.

In less than one second, pressures inside the booster go from zero to more than 800 pounds per square inch, causing the rocket's half-inch-thick steel walls to bulge outward and open the gap the two O-rings are supposed to seal. If the primary O-ring is burned away, there is a "high probability of no secondary seal capability" once the engine has fired for more than one-third of a second, Thiokol said.

The potential for this problem was known more than three years ago when NASA officials learned that ignition pressure could deform the joints, making it impossible for the backup seal to function. In February of 1983, NASA officially recognized the problem as posing the gravest risk to the astronauts, who have no safe means of escape while the boosters are firing.

NASA dealt with this by waiving the normal requirement for a fail-safe backup seal while it searched, for more than three years, for a corrective measure.

A 12-second videotape of the ignition shows a thick burst of black smoke near what appears to be the area at which the external fuel tank is joined to the right solid rocket booster, a quarter of the way up the rocket. According to NASA, the smoke appeared at about 0.67 seconds after ignition.

A NASA official told journalists here that the task force examining computer data from the launch has placed "special emphasis on operation of the SRB and external tank at the moment of liftoff."

The pictures and videotape, taken by engineering cameras near the pad, were released as the president's commission investigating the shuttle explosion concluded its first day of briefings at the Kennedy Space Center here.

The commission spokesman, Mark Weinberg, said the members received "extensive and detailed" time-line data showing the chain of events leading up to the explosion.

The pictures were released to the media at the request of the presidential commission, United Press International reported.

The release of the photographs today came at a time when increased effort is being made to find the right booster, which is believed to be lying on the floor of the Atlantic Ocean.

Although both NASA and the Navy have issued contradictory and often confusing information on the progress of that search, sources involved in the investigation now say that the location of the SRB has been firmly established by sonar readings, and that the recovery will begin as soon as it is photographed in detail.