New findings, not yet published in scientific literature, challenge one of the most startling recent claims in astrophysics -- that there exists in space an unprecedentedly heavy object exerting the combined gravitational pull of a thousand galaxies.

John Maddox, editor of Nature, the prestigious British journal that published the original claim in its May 8 issue, wrote an editorial in yesterday's issue advising readers that the rival information is to be published in two weeks.

"Advance notice of these measurements is being provided now, with the consent of the authors," Maddox wrote, "merely because of the excitement generated by the original measurements."

Maddox said that, while it is not certain the original findings were wrong, if they are, "there will be a widespread sense of disappointment that a potentially fascinating phenomenon has so quickly vanished."

Ironically, the issue of Nature that carries the editorial also includes two articles by prominent physicists examining implications of the original claim.

One deals with the possibility that the mysterious object is a black hole more powerful than any previously imagined, and the other is about the prospect that the object is what astrophysicists call a cosmic string.

It was this bizarre possibility that excited many scientists because, although cosmic strings are predicted by modern cosmological theories, none has been found.

A cosmic string, which some scientists refer to as a "crack in space," has a diameter less than that of a subatomic particle but may be trillions of miles long. Each inch of its length would exert the gravitational pull of millions of tons of matter.

The original report, by eight scientists under the leadership of Princeton University's Edwin L. Turner, did not claim proof that the object exists but simply reported what appeared to be a gravitational lens of unprecedented strength.

Weaker gravitational lenses are known to exist because of the effect they have on light traveling from a distant star or quasar, the nucleus of a galaxy.

Gravity, as Albert Einstein's theories of relativity showed, can bend the path of light just as a glass prism does. Thus, if a powerful source of gravity lies directly between telescopes on Earth and a distant star, it can split the light, producing a kind of mirage with two or more images of the star.

Scientists can usually tell that the multiple images are of the same star if the light's spectra are the same for all images. Different stars produce different spectra, varying with molecular composition and other factors.

Turner and his colleagues reported finding two images of a quasar with almost identical spectra for the wave lengths of light in the visible part of the spectrum. The images were so widely separated in the sky that the finding implied existence of an intervening gravity source more powerful than anything imagined.

The rival findings, by P.A. Shaver and S. Christiani of the European Southern Observatory, state that, in other parts of the spectrum, specifically the ultraviolet, the spectra differ. Therefore, they say, the two images represent two different quasars. If so, there is no gravitational lens.

The observatory, in Chile, is operated by a consortium of European countries.

"I don't think this necessarily contradicts our data," Turner said in an interview yesterday, "but it does weaken the case for there being a gravitational lens."

Turner said, however, that ultraviolet spectra are notoriously difficult to measure accurately because molecules in space, between the telescope and the distant object, also emit ultraviolet radiation. Signals from these sources can distort the readings.

He said further work would be needed to show whether the ultraviolet "noise" is mixed with ultraviolet signals from the two images. If the differences turn out to be attributable to these extraneous signals, the case for a gravitational lens would stand up.