SAND SPRINGS, Okla. (AP) _ The plaque at Hissom Memorial Center, a state institution for the mentally retarded, reads: ''Dedicated to the Infinite Care of Oklahoma's Children.''

But some parents and educators think Hissom's residents, 80 percent of whom are severely retarded, would be better off in group or foster homes. And they believe the 245 residents aged 22 or younger, still legally entitled to public education, should be schooled alongside regular classmates.

To them, Hissom is a relic, living on despite the 12-year-old federal Education for All Handicapped Children Act, which mandated public schooling for the handicapped in the ''least restrictive environment.''

On July 24, U.S. District Judge James Ellison agreed, issuing a 61-page plan of community integration and ordering Hissom to close in four years. State attorneys have indicated they will appeal, having failed to agree with the plaintiffs on just how to integrate Hissom students into public schools.

But some parents, and some Oklahoma educators, aren't convinced that closing Hissom will leave its residents better off.

Sunny Tiedemann says her son, Allen, has found happiness at Hissom.

''We found that we had additional problems with Allen because he was in community education,'' she said. ''He saw himself as so different. These differences are so much more visible to the retarded child when he is in a 'normal' situation. He started having emotional problems.''

But Judy Berry, an associate professor of psychology at the University of Tulsa, wants her 17-year-old son, Doug, in public school.

''There will be moments when kids are teased. That's still no reason to hide behind the walls at Hissom,'' she said. ''In a way, our kids are going to have to be pioneers of that.''

''Oklahoma is behind other states in even trying to develop that kind of (integrated) system,'' said Julia Teska, Hissom's superintendent. ''It can be done here. It's not going to happen overnight.''

At Hissom, education may consist of learning to turn on a radio, or mastering a mouth movement so food can be swallowed without choking.

In one classroom, therapists help a girl learn balance by bouncing on a huge inflatable mattress.

''You're not talking about getting them to know their colors, say their ABCs and read 'Dick and Jane,''' said Teska, who said she was afraid many public schools weren't prepared to deal with such youngsters.

Hissom has a staff of 68, including 30 teachers who are employees of the Sand Springs Public Schools. The state Department of Education provides some funding for the students; the Department of Human Services picks up the remainder.

Academic costs for a student at Hissom are about $4,600, compared to about $2,900 for regular students in Sand Springs schools, said Sand Springs Superintendent Wendell Sharpton. Adding in housing and other residential expenses brings the yearly cost at Hissom to about $20,000 per pupil.

Sharpton worries that Sand Springs would wind up totally responsible for Hissom students if the school closes. The state education department filed a petition Oct. 7 asking a federal judge to order Sand Springs to educate more Hissom residents in public school.

But Louis Bullock, a Tulsa attorney representing parents who brought the lawsuit, said that in the past the state has looked for ''the cheapest, easiest way'' to deliver educational services to the retarded.

''That is simply not adequate under the law,'' he said. ''The most profoundly retarded are those who most need to be in a community school. They learn by imitating and mimicking other people.

''You're talking about teaching them functioning living skills, how to have some independence, some liberty that they can enjoy,'' Bullock said. ''The technology and expertise exists. You don't know what their potential is until you test it.

''Separate was never equal,'' he said. ''We need to relearn the same lesson regarding the handicapped. Like so many things in life, it doesn't come naturally. We are all the loser, by segregating the handicapped.''