WASHINGTON, May 16 — Scientists working with the Defense Department have found evidence that a low-level exposure to sarin nerve gas — the kind experienced by more than 100,000 American troops in the Persian Gulf war of 1991 — could have caused lasting brain deficits in former service members.

Though the results are preliminary, the study is notable for being financed by the federal government and for being the first to make use of a detailed analysis of sarin exposure performed by the Pentagon, based on wind patterns and plume size.

The report, to be published in the June issue of the journal NeuroToxicology, found apparent changes in the brain’s connective tissue — its so-called white matter — in soldiers exposed to the gas. The extent of the brain changes — less white matter and slightly larger brain cavities — corresponded to the extent of exposure, the study found.

Previous studies had suggested that exposure affected the brain in some neural regions, but the evidence was not convincing to many scientists. The new report is likely to revive the long-debated question of why so many troops returned from that war with unexplained physical problems. Many in the scientific community have questioned whether the so-called gulf war illnesses have a physiological basis, and far more research will have to be done before it is known whether those illnesses can be traced to exposure to sarin. The long-term effects of sarin on the brain are still not well understood.