Two years ago today, the space shuttle Challenger exploded on national television. Since then, the 73 seconds of fatal flight have never left the microscope.

The report of a presidential commission was issued in June 1986, but it did not end the scrutiny, especially for a persistent Virginia engineering consultant who still argues that errors have been sewn into the fabric of the official record.

Ali AbuTaha is a self-employed consultant who has worked in aerospace, satellite, computer and video engineering for 20 years. Unlike most armchair Challenger troubleshooters, he has studied more than 3,000 pages generated by the Rogers Commission, which investigated the accident.

AbuTaha contends the Rogers Commission investigators took the wrong tack when they concluded that O-rings caused the fatal explosion. He believes a pre-existing crack near the aft joint of the right solid rocket booster led to the disaster.

By filtering away the glare of sunlight and rocket exhaust from his home video recording, AbuTaha saw fire striking the right wing and main engines of the Challenger seconds after it was launched into the Florida sky. He contends that the steadily growing leak of fire was obscured by the lighting and the shuttle's external tank, so the commission did not confirm the "first evidence of flame" until 58.7 seconds into the flight.

AbuTaha claims his continuous-leak theory helps explain other anomalies, including the inability of recovery teams to find some missing shuttle pieces off the Florida coast. After reviewing AbuTaha's preliminary findings early last year, the National Aeronautics and Space Administration wrote a three-page analysis of his work that ended by saying, "NASA finds no evidence in any of your analyses that could change the original sequence of events or the cause of the accident."

But the controversial engineer's work recently prompted a Pentagon intelligence official to try to get him an audience at NASA.

David Acheson, the only commissioner to review AbuTaha's video evidence, said his theories hinge on questionable glints of light.

Myron Uman, director of the National Research Project, which is overseeing the redesign of the next shuttle, said AbuTaha simply "doesn't understand much of the stuff he is doing." Even if some of AbuTaha's findings are correct, they would not affect future shuttle flights, Uman said. Preparation for NASA's 26th shuttle launch, scheduled for August, has included exhaustive testing of the boosters beyond the O-ring problems, he added.

An aerospace scientist in private industry, Dr. Andrew Meulenberg, speculates NASA has been using some of AbuTaha's findings "without admitting it."

The official NASA chronology contains no unusual occurrence between a series of puffs of black smoke three seconds after liftoff and the first visible flame 55 seconds later. "NASA says something happened at the beginning and at the end and nothing in between," said Meulenberg. "AbuTaha has basically filled in the blanks."