Experts performing autopsies on the astronauts killed in the Challenger explosion probably will be able to identify the remains, but pinpointing the exact cause of death will be more difficult, according to specialists in forensic pathology, the branch of medicine dealing with violent death.

The Armed Forces Institute of Pathology (AFIP) team at work in Florida will X-ray tooth and bone fragments, perform chemical tests on tissue and analyze injury patterns to try to learn whether the astronauts died from the explosion, fire, toxic gases or from impact when their compartment hit the ocean surface.

Whether they find the answer depends on how much tissue is left to study after six weeks in the sea.

"This is a very difficult case to predict, because of the time interval and the fact that there was a fire and that they have been in water," said Dr. Douglas S. Dixon, associate chief medical examiner of Massachusetts and former AFIP chief of forensic pathology.

Dixon and others interviewed said tissue is much better preserved in sea water than in air, and that if portions of the crew cabin remained protected from fish and other scavengers the remains might be in fairly good condition. The crew compartment was found in about 100 feet of water. Water temperature at that depth and location averages 71 degrees, according to the National Oceanographic Data Center.

Dixon, who has worked on crash investigation teams at the AFIP, said pathologists will try to reconstruct fracture patterns from bones that are found and, if possible, take samples of bone marrow and internal organs to measure levels of carbon monoxide, cyanide and other toxic chemicals generated during fires. They also may be able to assess injuries to internal organs such as the spleen or liver.

From such evidence, the pathologists may be able to decide whether the astronauts died from injuries during the explosion and fire or survived until the shattered space shuttle hit water.

"If there is thermal damage, that does not necessarily mean they died of fire," Dixon said. "They could have died of injuries and later been burned. I doubt that they came all the way down alive and drowned."

From the injury patterns, he said, pathologists should be able to estimate the g-forces at impact and judge how seats, safety harnesses and cabin walls performed during the accident.

Matching teeth with dental records probably will provide the best means of identification, because teeth are considered second only to fingerprints for that purpose, according to Dr. Ali Z. Hameli, chief medical examiner for the state of Delaware and a consultant to the Justice Department last year in the identification of accused Nazi war criminal Josef Mengele.

"Identification should not be very difficult. They know who the missing people are and they have medical and other information," he said. "The question is whether the remains of all seven astronauts are there, or some are not."

An X-ray of a limb bone can often reveal the age and sex of its owner, and blood typing and chromosome tests can aid in tissue identification, according to Dr. Ross E. Zumwalt, director of forensic pathology at the Cinncinati coroners' office.

"I was rather surprised when they said they found the remains," Dixon said.

"It's good," he added, "because it gives the families something to focus on, finally. When you've got a body, you can bury it and grieve and be done with it."