WASHINGTON (AP) _ Dinosaur DNA probably could not survive longer than 100,000 years unless it had been preserved in amber, according to California scientists who have found a way to test specimens for the presence of ancient genetic matter.

Jeffrey L. Bada of University of California, San Diego, said that chemical changes in the amino acids in fossil samples shows that in an environment with any water at all, genetic material from dinosaurs would have wasted away in just a few thousand years. The giant animals became extinct about 65 million years ago.

In a report to be published Friday in the journal Science, Bada said that amino acids in a fossil change their chemical character through a process called racemization.

Bada said the only ancient specimens found that contain confirmed DNA were some removed from the gut of insects that had been preserved for millions of years in amber, the harden sap of ancient trees. Amber, he said, apparently can absolutely seal the material away from water, which causes rapid transformation of the amino acids.

``The amino acids in the amber looked just like the amino acids you would find today, even though it was 130 million years old,'' said Bada.

Ironically, dinosaur blood in the gut of insects preserved in amber was the source of the DNA used to clone dinosaurs in the fictional book and movie ``Jurassic Park.''

Amino acids in living animals are in what is called a left-handed form. After the animal dies, the amino acids begin changing until half of the material is of a right-handed form and half is left-handed.

Bada said the rate of this racemization is known. As a result, by measuring the ratio of right- and left-handed amino acids, researchers have a type of deterioration scale.

Since DNA changes at about the same rate as the amino acids, said Bada, ``this test is a proxy for DNA. It provides a way to determine if a fossil may contain preserved DNA.''

Bada and his colleagues discovered the racemazation scale by analyzing a number of ancient fossils, ranging in age from 17 million to 65 million years old.

Included were fossils found by Brigham Young University researcher Scott Woodward, who claimed last year that the remains contained DNA from dinosaurs. Woodward's report was met with skepticism.

Now Bada said his test cuts down the Woodward claim.

``What we have shown is that you cannot get meaningful DNA out of dinosaur fossils,'' Bada said in an interview.

Woodward did not answer calls at his Brigham Young office, but he told Science that _ based on Bada's findings _ the prospect of finding dino DNA ``looks bleak.''

Another researcher, Rob DeSalle of the American Museaum of Natural History, told Science that the Bada study was ``really nice work'' that will be useful in the study of ancient fossils. He said it should allow scientists to quickly determine if a sample has measurable DNA without damaging the specimen.