Insisting that a flawed solid rocket booster would have exploded instead of flying on, several former executives from solid rocket fuel companies are questioning National Aeronautics and Space Administration reports that the Challenger's right solid rocket booster was spraying a "plume" of flame that could have touched off the explosion.

"In my experience, a solid rocket machine that leaks almost immediately suffers a catastrophic event," said former Morton Thiokol senior vice president Antonio Sovoca, who had been general manager of the company's Utah plant that makes the shuttle's solid rocket booster fuel.

Morton Thiokol, a $1.8 billion Chicago-based diversified specialty chemical company, is the prime contractor for the shuttle's solid rocket boosters.

Several observers have speculated that heavy vibrations and/or a crack in the rocket booster's fuel could have led to a burnthrough of the booster's steel casing. That would have created a virtual blowtorch that could have ignited the external fuel tank of the shuttle.

Sovoca dismissed assertions that cold Florida weather might have rendered the fuel vulnerable to vibrations that could generate cracks and flaws.

"Propellant samples are taken daily," he said. "They are tested at temperature extremes beyond those required."

Similarly, Harold W. Richey, a chemist who retired as Thiokol president in 1977, and Billings Brown, an engineer who resigned four years ago from Hercules Inc., an aerospace company, insisted that a serious leak in the rocket booster could not have lasted for the 14 seconds or more in which the photogrpahs indicated a plume of flame Jan. 28 when the shuttle exploded. A leak would have destroyed the volatile booster within five seconds, said Brown, who was Hercules group supervisor of the explosive hazards analysis group.

Brown, Richey and Sovoca pointed to observations that the boosters appeared to be flying normally after the Challenger explosion.