NEW YORK (AP) _ New evidence of a previously unknown force in nature called the hypercharge force could spark an important revision of existing physical theories, researchers say.

''I think it's a very important result if it's right,'' said Robert Dicke of Princeton University, one of the world's leading authorities on gravitation. ''It tells us something about elementary particles, and it also requires a modification of our theories of gravitation.''

Some physicists expressed skepticism about the evidence for the new force, but Dicke said he found it ''fairly convincing,'' adding that ''with anything as revolutionary as this, you would like to see new and improved experiments.''

The evidence for the new force, which tends to counteract the force of gravity over short distances, comes from a new analysis of a classic 60-year- old physics experiment called the Eotvos experiment.

In 1922, Roland von Eotvos and colleagues in Budapest, Hungary, claimed to have confirmed Galileo's results in a classic experiment in which measurements of objects of different weights showed that gravity acted equally on all of them.

Eotvos had blamed small errors in his measurements on the limitations of his equipment.

Ephraim Fischbach of Purdue University in West Lafayette, Ind. and his colleagues looked at those small errors and concluded they were not errors, but rather discrepancies that the scientists now attribute to the hypercharge force.

A report of the findings was published in the Jan. 6 issue of Physical Review Letters by Fischbach and his colleagues - Daniel Sudarsky, Aaron Szafer and Carrick Talmadge from Purdue, and Sam Aronson from Brookhaven National Laboratory on Long Island, N.Y.

Fischbach noted that the new force does not challenge Einstein's theory of gravitation. What Einstein said about gravity remains true, although Einstein said nothing about any other possible force like the hypercharge force.

The peculiar force would allow a feather to fall to the ground faster than a lead brick, in the absence of wind resistance.

Four hundred years ago, Galileo disproved the common-sense notion that heavier objects fall faster than lighter ones. Legend has it that he dropped two objects of different weights from the top of the leaning tower of Pisa. Both fell at the same rate.

The newly discovered force would slow the fall of the heavier object by a very small amount.

Four forces are now known in the universe: gravity, electromagnetism, and two sub-atomic forces called the strong force and the weak force. The hypercharge force would be the fifth.

Fischbach said he is not the first to find evidence of such a force. Frank Stacey of the University of Queensland in Brisbane, Australia, has during the last few years reported finding discrepancies in gravitational measurements. Fischbach now explains those discrepancies as further evidence of the hypercharge force.

''I myself think the evidence from all of the experiments is pretty convincing,'' he said Wednesday in a telephone interview from the University of Washington in Seattle, where he is on sabbatical from Purdue.

''But I agree that many, many experiments have to be done to check details and many theoretical analyses have to be done to support this.''

The hypercharge force gets its name from a characteristic of sub-atomic particles called hypercharge. Just as some sub-atomic particles carry an electrical charge, some also carry a hypercharge.

Unlike gravity, which can act on objects hundreds of millions of miles apart, the hypercharge is believed to act only at distances of several thousand yards or less, Dicke said. Thus it does not affect gravitational calculations of the movement of celestial bodies.