John Edward Denny, 38 and mentally retarded, lives in the Montgomery County home of his 79-year-old mother, who is afraid of what will happen to her son after her death.

Twenty-three-year-old Sheila A. Reeve, also mentally retarded and living at home with her parents, has forgotten how to make her bed in the two years since her federally guaranteed educational program ended.

Both are on waiting lists to move into group homes for the mentally handicapped, and both are plaintiffs in a suit filed yesterday against the State of Maryland, alleging a lack of adequate residential and training programs for mentally retarded persons over the age of 21.

The suit is indicative of legal and legislative efforts across the country aimed at improving programs for mentally handicapped adults, who, like Reeve, have recently lost the protection of a 10-year-old federal law that guarantees educational programs until the age of 21.

The lawsuit, filed in Montgomery County Circuit Court, names as defendants Gov. Harry Hughes and several other state officials, charging them with interfering with the development of, and seeking placement in programs for, three plaintiffs.

"These people are symbolic of the urgent needs so many, many people in the community are facing," said William D. Baber, executive director of the Montgomery County Association for Retarded Citizens.

Baber said there are more than 400 people in Montgomery County on waiting lists for residential programs. There are about 2,000 mentally handicapped people, most of them over age 21, on waiting lists for residential services in Maryland, according to Elmer L. Cerano, executive director of the Association for Retarded Citizens of Maryland, which sponsored the lawsuit. There also is a waiting list of nearly 1,300 for vocational day programs in the state, he said.

"We're just seeing the first generation of students exiting school systems after PL 94-142," said Cerano, referring to the federal law guaranteeing education for handicapped children. "In good solid numbers, people who have benefited from that program, plus those with elderly parents . . . have come together and are really screaming."

John Denny has been on a waiting list for a residential group home for nearly three years.

"As long as his father and I lived, we hoped to be able to take care of John ," said his mother, Mary Denny. After her husband died in 1975, she said, "then I felt like, well, I might go at any time myself because I'm not young. I just felt like I needed to make some kind of preparation for John.

"All along, I had asked for a group home . . . but I guess I didn't push hard enough," she said.

The third plaintiff in the suit is Pearl I. Wymer, 58, who lives with a 53-year-old sister in Montgomery County. Wymer has been on a waiting list for a residential group home since 1982, according to the suit.

"Based on the history of growth of community services, it could take a person 30 years to get off the waiting list," said Baber. He said his association "believes that every person with mental retardation has a right to leave their parent's home . . . to be able to live in small community-like settings, with full access to the life of the community."

A spokesman for Hughes said the governor would not comment on the lawsuit because he had not seen it, but said that, during his administration, Hughes has "more than tripled the slots for deinstitutionalization and treatment for the mentally handicapped."

Filing the suit yesterday was attorney Ralph J. Moore Jr., who led the fight for a 1973 Maryland law that required the state to pay the full cost of educating handicapped children.

Maryland was among the first states to pass such a law and that success bolstered efforts to pass a federal law two years later.

The current suit argues that a Maryland law covering the well-being of all mentally handicapped persons requires the state to place those individuals in proper programs and failure to do so violates federal constitutional protections.

"Our real hope as an organization is that the state will develop a plan for correcting this waiting list problem," said Cerano. He said that, while the programs are to expand by 300 this year, the waiting list grows by the same number each year.