Mike Epstein had never had an accident in two years of driving. Then last month, he struck a 15-year-old boy who was crossing a suburban Maryland street, fracturing the youth's skull and hospitalizing him for a month.

Police blamed the boy's carelessness for the mishap, and Epstein, 28, a low-level employe of the federal government, never was charged.

Despite that, Mike Epstein may lose his driver's license. The reason: a police officer at the scene noted that Epstein "appeared to be mildly retarded" and, in the patrolman's opinion, was unable to drive a car safely.

As a result, Epstein has been summoned to appear before a state review panel next month to determine whether his condition is grounds to revoke his license. It will be an apparently unprecedented proceeding for a retarded Maryland resident and one of the first such cases in the nation.

"The officer presumed that there was something wrong with him because of the way he looked," said Robert Plotkin, senior attorney with the nonprofit, Washington-based Mental Health Law Project, which is monitoring Epstein's case closely.

"If [the officer] had used race or sex as a basis for his judgment, people would be up in arms about this. Cars are crucial for modern life. If we're really concerned about driving standards, then we ought to retest everyone."

Maryland officials reject any suggestion of discrimination, saying that Epstein will be judged solely on his ability to drive a car, not on any label of mental handicap.

Epstein earns $10,740 a year as a GS 3 in the U.S. Office of Education, filling stockroom orders, copying documents and delivering papers within the federal bureaucracy. He talks with great difficulty because of a speech defect he said he is working to overcome.

Sometimes his hands hang limply in front of him and he walks with a slightly knock-kneed gait.

"I didn't want my friends to drive me anymore," Epstein said of his decision to seek a driver's license. "I wanted to be independent."

Epstein twice failed the "practical" part of the Maryland drving test, but finally passed it two years ago after using state rehabilitation funds to study at a private driving school, he said. Maryland officials at the Department of Transportation said Epstein's driving record was unblemished.

"The kid was taking his time crossing the street, he couldn't make up his mind, and then I hit him," Epstein recalled in an interview."My first thought was, why did it happen to me? I felt terrible about it. I called the hospital every day to see how he was. I sent him a get-well card, but was afraid to sign my name, so I signed it, 'From Friends,'" he said, sitting in an office at the Office of Education's handicapped affairs section.

Epstein is one of an estimated 6.2 million Americans who will be labeled "mentally retarded" at some point in their lives, according to federal figures. "Many retarded persons are like Epstein, able to lead comparatively regular lives by working around their handicaps, which often includes physical problems, these officials added.

"I pay $189 for my apartment," at Inwood Gardens in Silver Spring, which rents mainly to people with handicaps. "I am learning sign language so I can talk to the people who are deaf," he said.

Epstein has worked for the federal government since graduating from Montgomery County's Rock Terrace High School in 1970. The cause of his difficulties, present since birth, are not known, a situation found in three out of every four cases of mental limitations, officials added.

According to Don Weinberger, principal of Rock Terrace, which provides education for handicapped children, "It usually takes longer for mentally retarded people to acquire the social judgments needed to drive. Each year several of our graduates come back to say they are now driving. But some retarded people will become so scared [once they have their license] that they stop driving of their own accord."

Three years ago Epstein successfully petitioned federal personnel officers to move him from the category of "mentally retarded" to "physically impaired," which Epstein felt more accurately reflected his difficulties in speaking, not thinking, according to Scott Mueller, of the Office of Handicapped Concerns.

Then Epstein began driving.

Constantine N. Zuras, of 1211 Arcola Ave., in Silver Spring, was crossing University Boulevard near Sligo Creek Parkway at 4:30 p.m. on Saturday, April 5, when he was struck by Epstein's car, according to Montgomery County police officer Joseph C. Niebauer.

"Pedestrian error caused the accident," Niebauer said yesterday, "but from talking to Epstein afterwards I concluded he just should not be driving a car."

Niebauer filed a recommendation with the Maryland Department of Transportation that it reexamine Epstein's qualifications for a license. Epstein "appeared to be mildly retarded" and had "extreme difficulty in communicating what had occurred," his report stated.

Joseph L. Lupinek, director of the Maryland Transportation Department's administrative adjudication section, said the Epstein case is the first out of hundreds his department hears annually to involve mental retardation as a possible reason for license revocation.

At the hearing scheduled for June 11, Epstein will be interviewed by a state hearing officer, and possible by a panel of medical experts. If they choose, the specialists may test his motor coordination and physical ability to handle a car, Lupinek said. Epstein's license can be left untouched, suspended, or revoked, he added.

Epstein, meanwhile, said he will seek legal help if his license is taken away. "I don't drive anymore now," he said this week. "I'm too nervous."