The White House has gathered seven outside experts on atomospheric science to discuss whether natural events might have caused the atom bomb-like flash in the skies south of South Africa in September.

White House science adviser Frank Press, who convened the first of two days of meetings in his office yesterday in the Old Executive Office Building, declined to identify any of the experts, saying that they might be at work for months and that identifying them might compromise their work.

A U.S. Vela surveillance satellite spotted a double pulse of light characteristic of a nuclear explosion in the vicinity of South Africa in late September, but U.S. intelligence could find no corroborating evidence of an atomic explosion.

Sensors on the satellite that would have detected a release of neutrons, gamma rays and x-rays apparently had been turned off to save power on the satellite and prolong its life. The Vela was aging, having been put into orbit in 1970 to watch for violations of the global treaty banning atmospheric tests.

A few days after the initial reports of the Sept. 22 phenomenon, which was described as a probable nuclear test, the Air Force Technical Applications Center and the CIA reported finding acoustic evidence from listening posts in widely separated parts of the world that seemed to confirm an explosion. After further study, however, they withdrew this conclusion, according to official sources, and reported that the earlier evidence might simply have been commonplace random background noise.

No seismic evidence was recorded anywhere in the world of a nuclear explosion. More importantly, search aircraft flying over the Indian and South Atlantic oceans have found no evidence of radioactive debris in the atmosphere that would have been left by a nuclear explosion.

The seven experts were brought to Washington to discuss alternate explanations for Vela's observation, such as a "superbolt" of lightning, a meteor entering the atmosphere or a freak combination of the two.

A White House source said the experts so far have not ruled out any of those explanations but cast some doubt on them.

Vela has seen many superbolts in its nin years in orbit, always as a single flash of light and not the double flash it saw in September. On no fewer than 41 previous occasions did Vela see the double flash and it always was a French or Chinese nuclear test in the atmosphere.

Regarding the theory of a meteor burning up, there were no reports anywhere that a meteor large enough to generate that much light had entered the atmosphere, the same source said.

The source said the panel also discussed whether the doubleflash was sunlight glinting off another satellite or a spark or electronic malfunction inside the Vela. The source said neither of these possibilities has been ruled out.

"There is a remote chance," the source said, "that the satellite could have malfunctioned once in a way that we did not see again. We're looking at that possibility."

Last week, the State Department announced that the satellite had seen what appeared to be a nuclear explosion and suggested South Africa as the source.South Africa has vehemently denied that it triggered an atomic explosion.