A series of unexplained massive, high-altitude "explosions" that has alarmed residents along the New Jersey shore and in South Carolina for several weeks were reported again yesterday as government and scientific authorities shrugged their shoulders in bafflement over a possible cause of the phenomenon.

But nobody was at a loss for theories.

Explanations offered - and quickly denied - included meteor showers, thunderclaps, sonic booms, offshore oil rig explosions, top secret military experiments, Soviet submarines testing polaris-like missiles, re-entry of a satellite, a prelude to a devastating earthquake and pranksters with huge helium-filled balloons that explode.

One government scientist said, "Maybe Steven Spielberg is putting together a new movie," referring to the director of the currently popular science fiction film "Close Encounters of the Third Kind."

The Federal Aviation Administration all but ruled out sonic booms caused by aircraft, and defense officials denied that any secret military experiments were being conducted in the atmosphere.

Scientists dismissed meteor showers or thunderclaps as a possible cause of the mysterious atmospheric disturbances, pointing out that the explosions were so intense they were recorded simultaneously on seismographs as far apart as Boston and Charleston, S.C.

A seismologist at Boston College's Weston Observatory, Edward-Chiburif, said he had recorded ground waves immediately following some of the atmospheric disturbances, and that the tremors were equivalent to a Richter Scale reading of between 3 and 3.3.

The Richter Scale is used to measure the intensity of earthquakes. The 1906 San Francisco quake registered 8.3 on the scale.

"I think, personally, that they are sonic booms. I cannot for the life of me propose any explanation," said Chiburif.

But FAA officials in Washington said none of the listening devices the agency monitors along the Eastern Seaboard detected any sonic booms when the explosions were reported on seven different occasions since Dec. 2.

"We haven't ruled out sonic booms, but we don't believe that is it," an FAA spokesman said.

Moreover, officials at the Air Force North American Air Defense Command in Colorado Springs, Colo., denied that there were any supersonic military flights during the period of the explosions.

Similarly, officials of the National Aeronautics and Space Administration said the phenomena could not the explained by re-entry of rockets or any other space activity.

What some government officials were sure of, however, was that solving the mystery is not their responsibility.

"Nothing we've done or are doing could cause such a phenomenon. National security isn't involved, and we're not investigating it," said a Pentagon spokesman.

An FAA spokesman said, "We're convinced there's no danger to aircraft, and we're not conducting a formal investigation."

A NASA official said the space agency was not investigating the explosions because it has not been asked to.

Even if they could not explain the causes, no government officials nor scientists attempted to deny that intense atmospheric disturbances causing loud noise has occurred repeatedly in recent weeks.

Two of the explosions - one reportedly accompanied by bright lights in the sky - were observed in New Jersey Wednesday and early yesterday, while another was reported in South Carolina yesterday.

Similar explosions were reported along a 25-mile-long stretch of the south New Jersey shore and simultaneously in the Charleston, S.C., area on three previous occasions, beginning on Dec. 2.

The explosions, according to residents and police authorities, rattled windows for a few moments at a time, but caused no damage.

William Doan, director of atmospheric sciences at Columbia University's Lamont-Doherty Observatory in Palisades, N.Y., said his microbarograph instruments picked up "extremely intense acoustical waves" approximately 30 miles south of Long Beach Island, N.J.

Donn, in a telephone interview, said the origin of the explosions was not seismic - caused by any underground disturbance - and could not have been the result of a sonic boom.

"It has a very different signature than a sonic booms.

He said the strongest of the explosions was equal to the force of 10 tons of dynamite, or equivalent to the big oil refinery explosion that rocked Linden, N.J., in 1970.

In contrast to a number of cautious explanations offered by some scientists interviewed, Donn suggested that some sort of military activity caused the explosions.

When asked about the Pentagon's assertions, Donn said, "Well, nobody knew about the atomic bomb unless they were directly involved in it."

He stressed, however, that he was as gaffled as others in the scientific community, noting that historians have long recorded such unexplained atmospheric phenomenon, such as the legendary "Seneca Guns" in upstate New York Seneca Lake and the Lough Meagh, Ireland, unexplained "rumbles."

Dr. Joyce Bagwell, a seismologist at Baptist College, Charleston, S.C., said her instruments have picked up strong readings on the same days the sound was observed in New Jersey, but she offered no explanation other than a sonic boom.

"We see indications of some odd disturbances. It's similar to sonic activity, but I don't know what it is," she said in a telephone interview.

Richard Golob, director of the Center for Short-lived Phenomena in Cambridge, Mass., said "We're as baffled as the scientific groups and government agencies. There's no way to correlate it to a natural phenomenon. If it's man-made, we have no good understanding what it might have been."

Golob, stressing that he was suggesting no such danger, noted that historical records show that major earthquakes often are preceeded by similar atmospheric phenomenan.