Ergot, a poisonous fungus that grows on rye and produces hallucinations, was a major cause of the Great Fear that swept the French countryside and helped speed the French Revolution in 1789, according to a new report by Mary K. Matossian, a University of Maryland historian.

Matossian, an associate professor who has specialized in the importance of fungi in history, said ergot has been used in recent years to make the hallucinogenic drug LSD or lysergic acid diethylamide.

"I think I'm on to something big," Matossian said yesterday in an interview. "There are bizarre episodes in the human past which we just can't explain any other way except that large numbers of people were eating infected rye bread."

In a previous report, published last summer, she said ergot poisoning was responsible for the widespread outbreak of visions, convulsions, and hallucinations that culminated in the witch trials of 1692 in Salem, Mass.

She said it also caused the Great Awakening in southern New England in 1741 and held down population growth in much of Europe until the late 18th century.

Other historians, though are skeptical.

"There's no doubt her research is good," said John Duffy, a history professor at the University of Maryland. "But I think she's making a grand theory of history out of it. She's applying it to too many things, and that's too simple."

Matossian's new paper, presented this week at the annual meeting in Washington of the American Historical Association, includes weather reports, doctors' reports, maps of French cropland, and a chronology of peasant outbreaks to support the thesis that ergot caused the Great Fear of late July and early August of 1789 that panicked French peasants.

The fungus grows on rye plants in cool, damp weather, Matossian said, conditions which prevailed that year in northern France where rye bread was the staple of the peasant diet.

"Weeping and shouting, the peasants fled into the woods to hide," she said. "Many women had miscarriages, and people blamed the rich for creating the disturbances" even though the rapes, massacres and fires of which they heard were largely imaginary. This panic among peasants, she said, helped produce a panic among property owners who dominated the French National Assembly. In one night, Aug. 4, the Assembly voted to dismantle most of the privileges of the Ancient Regime,

"I'm afraid I can't go along with all that," said Duffy, who was chairman of the convention panel on "epidemics and social change in Europe" where the paper was presented.

"The French Revolution was building for some years," he continued. "Yes, I think she has shown there was an outbreak of ergotism. But I think the Great Fear and the uprisings would have occurred whether there was ergot poisoning or not. It may have contributed to things. But you can't disregard the storming of the Bastille (which occurred in Paris on July 14, before the peasant panic) and a lot of other things."

A PhD graduate of Stanford and "card-carrying member of the Society of Mayflower Descendents," Matossian has taught at Maryland since 1965. She said her research projects have stretched from Soviet Armenia to family history in New England.

She said she came upon the idea that hallucinogenic fungi may have been important in shaping history about five years ago while doing research in the Connecticut State Library in Hartford. It was suggested to her, she said, by a young man she met at lunch.

"I'm not saying ergot is the only reason for the French Revolution," Matossian said. "That would be too simplified . . . There were the underlying deep causes of social injustice. But this was a precipitant. It was one of those things that pushed the course of events onto a radical track."