The Department of Energy, on the theory that people who oppose nuclear power may suffer from an irrational phobia, is paying a Rockville psychiatrist $85,000 to find out if their fears can be overcome.

The man who convinced the government that fear of a nuclear accident could be a psychiatric disorder is Robert L. DuPont, president of the Phobia Society of America and a frequent guest on television talk shows on subjects ranging from fear of flying to the dangers of marijuana.

DuPont, a former District of Columbia and federal official who operates a phobia treatment clinic, has thrust himself into the national nuclear power debate by arguing that people who fear nuclear power -- an estimated 40 to 50 percent of the public -- have a distorted view of the facts.

"This fear is widespread, irrational and aggressively exploited by the political opposition to nuclear electricity," DuPont wrote in the New York Daily News last year. "Fear persists despite the remarkable safety record of the nuclear power industry."

DOE spokesman Jim Merna said the noncompetitive grant suggested by DuPont Associates is for "a legitimate scientific inquiry . . . . There is a lot of opposition to nuclear power, and a lot of that opposition is based on fears. This is high-quality research being done by someone who is a pioneer in this field. We don't apologize for the study."

DuPont said yesterday that his study is not aimed at opponents of nuclear power, but at understanding whether "fear on anybody's part" is comparable to such phobias as fear of flying. He said it is "a paradox" that more people fear nuclear plants than more dangerous activities such as cigarette smoking.

"We want to understand what aspect they're afraid of, to see who thinks nuclear plants can blow up like a bomb, and to see whether information changes their level of fear," DuPont said. "I don't know how anyone can criticize the study when it's not finished."

A former head of the District of Columbia's narcotics treatment agency, DuPont directed the National Institute on Drug Abuse from the Nixon administration through the first 18 months of President Jimmy Carter's term. DuPont has appeared regularly on ABC-TV's "Good Morning America" and also heads the American Council on Marijuana.

In a paper presented to the Phobia Society this month, Robert Ackerman, a Phobia Society member and instructor at Downstate Medical Center in New York, accused DuPont of "a misuse of psychiatric labeling."

Ackerman said that DuPont "presents what is basically the nuclear industry's opinion regarding safety." He said that in an affidavit on behalf of a proposed nuclear plant in New York, DuPont depicted anti-nuclear activists "as phobia inducers infecting the populace with mental illness."

Other critics said the grant reflects the Reagan administration's views. Rep. Richard L. Ottinger (D-N.Y.) said the award is part of a pronuclear propaganda campaign that the DOE has been waging for 3 1/2 years. Janet Bearden of the Safe Energy Communication Council, a coalition of environmental groups, said the DOE is "trying to obscure the problems of nuclear power by shifting the blame to those who have legitimate concerns."

The phobia grant is the Energy Department's second to DuPont Associates. In 1982, the DOE paid the firm $16,000 to analyze the media's role in fostering nuclear fears and to "sensitize" public information officers about ways to avoid "contributing to unreasonable fears of nuclear power."

In the current study, DuPont is giving questionnaires on nuclear power to about 170 subjects, then surveying them again to see if their views changed after reading a nuclear energy booklet he has prepared.

The booklet, which says it is "not intended to take sides" in the debate, calls a major nuclear accident "a remote prospect." It says: "The record of nuclear power plants has been good in protecting both health and environment . . . . The small releases of radiation which have occurred . . . have been so low as to pose no threat to the public or to the environment, even to those people living close to the plants."

DuPont said yesterday that the booklet was "a statement of the facts of power plants' performance. If there's a factual error, no one has brought it to my attention."

In approving the grant, the DOE said, "The underlying hypothesis is that once people understand the principles governing the development of irrational fear, this fear will be substantially and permanently reduced."

DuPont is being assisted in the study by a former spokesman for the Atomic Industrial Forum, a nuclear industry trade group.