WASHINGTON, Oct. 14, 2004 - A federal panel of medical experts studying illnesses among veterans of the 1991 war in the Persian Gulf has broken with several earlier studies and concluded that many suffer from neurological damage caused by exposure to toxic chemicals, rejecting past findings that the ailments resulted mostly from wartime stress.

Citing new scientific research on the effects of exposure to low levels of neurotoxins, the Research Advisory Committee on Gulf War Veterans' Illnesses concludes in its draft report that "a substantial proportion of Gulf War veterans are ill with multisymptom conditions not explained by wartime stress or psychiatric illness."

It says a growing body of research suggests that many veterans' symptoms have a neurological cause and that there is a "probable link" to exposure to neurotoxins.

The report says possible sources include sarin, a nerve gas, from an Iraqi weapons depot blown up by American forces in 1991; a drug, pyridostigmine bromide, given to troops to protect against nerve gas; and pesticides used to protect soldiers in the region.

Dr. Joyce C. Lashof , the chairwoman of a presidential advisory group that reported in 1996 that there was no causal link between toxic exposure and the veterans' symptoms, said Thursday that she had not seen the new report. But Dr. Lashof said she was open to changing her views if the findings were based on solid new research and not advocacy by veterans' groups.

"We certainly weren't sure that our report was the definitive answer," Dr. Lashof, professor emerita of public health at the University of California at Berkeley, said. "It was based on the best evidence available at the time."

All the chemicals cited in the new study belong to a group called acetylcholinesterase inhibitors, which can cause a range of symptoms including pain, fatigue, diarrhea and cognitive impairment. Committee members said there might be minor changes in the report, a draft copy of which was obtained by The New York Times, but that the basic scientific findings would not change.

The committee says a search for medical treatments tailored to the new findings are "urgently needed" and recommends $60 million in federal funds for new research over the next four years. It says an estimated 100,000 Gulf War veterans, or about one in seven, suffer war-related health problems.

The report also says that understanding illnesses from the war will be critical in planning future military deployments and measures to improve domestic security. It calls for a reassessment of the use of pyridostigmine bromide.

Though some conclusions are hedged in careful language in the 135-page draft report, committee members said in interviews that they were consciously departing from the past scientific consensus and taking a strong stand on a politically and scientifically volatile subject.

"I would absolutely say it's a break from previous panels," said Dr. Beatrice A. Golomb, an associate professor of medicine at the University of California at San Diego, a member of the panel and its scientific director for much of its existence. "It reflects a different body of evidence, because more studies have come out. No one had gone to the scientific evidence on acetylcholinesterase inhibitors."

The new report, prepared for the federal Department of Veterans Affairs, draws conclusions that are essentially the opposite of those of the Presidential Advisory Committee on Gulf War Veterans' Illnesses, led by Dr. Lashof. That group reported to President Bill Clinton in 1996 that "current scientific evidence does not support a causal link" between the veterans' symptoms and chemical exposures in the Persian Gulf.

Instead, the earlier group said, stress "is likely to be an important contributing factor to the broad range of physical and psychological illnesses currently being reported by gulf war veterans."

Another panel of scientists convened in 1998 by the Institute of Medicine, a unit of the National Academies that focuses on health and medical advice, has produced a series of reports that generally point away from neurotoxin exposure as a likely cause of the veterans' illnesses.