Einstein's general theory of relativity is being challenged once again, this time by three astronomers from the University of Arizona who say they have found that the sun is not a perfect sphere as Einstein assumed it was when he developed his theory in 1916.

In a report presented yesterday to a meeting of the Royal Astronomical Society in Dublin, Arizona's Dr. Henry A. Hill said he, Dr. Philip Goode and graduate student Randall Bos used a solar telescope in the Santa Catalina Mountains northeast of Tucson to observe that there were fluctuations in the way the sun's edge darkens at the equator that strongly suggest the sun's equator is bulging and its north and south poles are flat. If true, that means the sun is more oblate than it is spherical.

"We believe we've found that the sun's interior spins once every 3.5 earth days, a brand new discovery that means the sun is spinning seven times faster in its interior than it is on the surface," Goode said yesterday from Tucson. "The solar exterior's spin rate is once every 25.4 earth days, a fact that has been known for some time."

Goode's observation is a fresh challenge to Einstein's almost sacred theory of relativity. There are two key elements to Einstein's theory-- one, that light from a distant star will be bent by the gravitational pull of the sun, and the other, that the sun's gravitational pull will have a distinctly measurable effect on the way the innermost planet, Mercury, revolves around the sun.

The numerous experiments conducted in the last 12 years to see if starlight is bent by the sun's pull all have verified Einstein. Two experiments showed that light from distant quasars was bent by the sun's gravity in just the way Einstein predicted, another that pulsar light did the same thing. A fourth experiment showed that radio signals from the Viking spacecraft that landed on Mars in 1976 were bent in the same way by the sun's gravity when Mars was on the other side of the sun from Earth.

More recent experiments bouncing radar signals off the planet Mercury back to radio antennas in California, Massachusetts and Puerto Rico also have verified that Mercury moves around the sun in just the way that Einstein said it would. The Arizona experiment is a challenge to these experiments as well as to Einstein.

"If the interior of the sun is rotating as rapidly as we say it is, then it makes an important contribution to the way Mercury orbits the sun," Goode said by telephone from his office in Tucson. "Einstein's theory of how Mercury orbits the sun is based on the assumption that the sun is a perfect sphere, which we do not believe it is. We think there is a 95 percent chance that there is a problem with Einstein's theory."

If there is such a thing as a scientific jury, it is nowhere near agreement with Goode and Hill that Einstein's theory is in trouble.

"There is still enough uncertainty with planetary orbits that nobody has measured Mercury's orbit with enough precision to say what it really is," said Dr. John D. Anderson of California's Jet Propulsion Laboratory, which has conducted many of the experiments to verify Einstein. "I accept the Arizona results but their deduction of solar oblateness is still theoretical, making their challenge to Einstein even more theoretical."

Most of the scientific discoveries that Einstein predicted in 1916 go unchallenged. The atomic bomb, nuclear energy, high-energy particle accelerators, fusion energy and precise long-distance space travel all are the results of Einstein's theory of relativity. What happens if he's a little bit wrong? Not much. Our atomic clocks might be off by an infinitesimal fraction of a second. Beyond that, says Dr. James Peebles of Princeton University, where Einstein taught, very little will change.

"There have been some slight errors in Einstein that have been modified through the years," Peebles said. "None of these things has altered the basic theory at all."