Scientists who investigated the Shroud of Turin last year said yesterday that its authenticity will be in doubt unless they are allowed to run tests to determine its age.

While conceding they had found nothing so far to prove the shroud is not authentic, the scientists agreed that none of the completed tests will mean anything unless the Vatican permits them to conduct a test that will fix the age by detecting the radioisotope carbon-14. The problem is that this test requires destruction of a tiny amount of the shroud.

"The key test for the shroud is its age," said Dr. Robert Dinnegar of the Los Alamos Scientific Laboratory in New Mexico and one of the leaders of the team that studied the shroud in Turin. "While none of us has found anything that disproves the shroud's authenticity, it's all meaningless without an exact age."

Dinnegar said two age-dating proposals were sent in July to the archbishop of Turin, who recently submitted them to the Pontificial Academy of Sciences in the Vatican for approval. One proposal came from the University of Rochester, the other from the Brookhaven National Laboratory in Upton, N.Y.

"Both proposals are destructive in that they need to destroy a few threads of the shroud to get an age," said Dinnegar. "The archbishop felt that since the tests are destructive, he ought to have agreement from higher authorities, which is why he submitted them to the Vatcan."

The Shroud is a yellowed strip of linen 14 feet long and three feet, seven inches wide that some believe to be the shroud the followers of Jesus wrapped him in after He was crucified. Found in France in 1350, the shroud has since been kept in a silver casket, locked by three keys, that is stored in a crypt behind the main altar of the Turin cathedral.

Forty American scientists visited Turin in October 1978 for six days of nondestructive tests on the shroud, which is imprinted with what appears to be the photograph-like image and bloodstains of a bearded man who was badly wounded and crucified.

The testing of the shroud included X-ray fluorescence, radiography, ultraviolet spectroscopy, infrared reflectance, visible fluorescence spectroscopy and computerized photographic enhancement and analysis. The tests were designed to look for fraud, to see if the bloodstains and image had been painted on the shroud long after the death of Christ.

The X-ray fluorescence tests turned up no signs of lead or zinc-based paints in the image, Dinnegar said. And the bloodstains appear to be authentic, he said.

Dinnegar said the image is so precise the scientific team could determine that it was of a man who had been crucified, who had suffered a deep and bloody wound in his side, endured what appeared to be 120 lashes with a whip and suffered numerous wounds around the head "that could have come from a crown of thorns."

"When we came to the marks on the image, we asked ourselves could these be wound marks?" Dinnegar said. "We investigated further and said yes, they could be. We then counted the wounds. They came to 120."

At least one member of the scientific team believes it is authentic. Said Thomas D'Muhala, president of Nuclear Technologies Inc., Amston, Conn.: "It's only my personal opinion, but I believe the shroud is authentic."

Others are not as sure. "I don't see how anybody can say the shroud is authentic," said Dr. Lawrence Schwalbe of Los Alamos. "Take the test for bloodstains. I've learned something about the bloodstains but not enough to say they're bloodstains." Added Dr. Roger Morris of Los Alamos: "To say the shroud is authentic based on what we know today is too strong a statement. We need more evidence, especially on age."

If the Vatican allows the shroud to be dated, tests should show its age within 30 years. If it is authentic, its age should be about 1,946 years.

The team is preparing scientific papers on its investigation. They should appear late this year or early next year.