A board of outside experts named by the White House to decide whether an atomic explosion took place near South Africa Sept. 22 has ruled out almost every other explanation for the event.

In a meeting convened by the White House Office of Science Policy just before Christmas, the panel of seven unidentified experts concluded there was no reason to suspect that the Vela satellite which spotted the Sept. 22 event had malfunctioned, or that what the satellite saw was caused by an enormous strike of lightning, as another theory suggested.

"The signal the satellite saw still looks in every way like a nuclear explosion in the atmosphere," one White House source said. "The trouble is, we still have no absolutely no separate data that would corroborate that it was an atomic explosion."

The most solid data would be radioactive fallout from the explosion which took place (if it was an explosion) in the middle of the night Sept. 22 above a wide expanse of the South Atlantic and Indian oceans. The nearest country to the source of the explosion was South Africa, which led to wide speculation that the South Africans had exploded their first atomic bomb.

Late in November, New Zealand thought it had detected fallout in its rainwater, but officials retracted that statement shortly thereafter, saying they could not be sure. One organization in New Zealand that measures radioactivity around the countryside said it had seen no evidence of fallout.

Some scientists suggested the Vela satellite had made a mistake, either by malfunctioning or mistaking a "superbolt" of lightning in the clouds above the ocean for a nuclear explosion. The panel convened by the White House was asked to look carefully into each possibility.

At the meeting convened by the White House before Christmas, the outside panel just about ruled out these possibilities.

White House sources said the panel concluded the satellite was in excellent working condition. Each time the satellite was interrogated from the ground, the sources said, it returned the correct information. What's more, the satellite has never repeated its Sept. 22 observation, suggesting it saw a real event in the skies near South Africa that night.

The lightning superbolt was described as "unlikely," because its signature is nothing like what was written in the sky the night of Sept. 22.

What the satellite saw as a double pulse of light that is the characteristic fingerprint of a nuclear explosion, in which a fireball briefly disappears when the shock wave makes it opaque from space, then reappears when the wave dissipates.

The panel covened by the White House has also concluded that a lightning strike quickly followed by meteor burning up in the atmosphere does not explain the event of Sept. 22. Said one White House source: "The statistical chance of that happening got bad very quickly once we started looking at it."

Despite the evidence that an atomic explosion took place Sept. 22, the White House has not disbanded its panel of seven experts. The White House will convene the panel at least once more after it has researched even the remote possibility that the Vela satellite may have mistaken a double glint of sunlight off another satellite.