Ardell Lesti says her son has been chewed, bitten and beaten in the 12 years he has spent at Great Oaks Center, a facility for the mentally handicapped in Silver Spring now under investigation by the state for alleged improprieties, including resident abuse.

So it came as no surprise to her when, three weeks ago, she got a telephone call at work from institution officials who said an employe had been suspended for allegedly slamming an aerosol can against her severely retarded son's head and striking two other residents.

The employe, Cleveland Patrick Lynn, 35, of Wheaton, has been charged with battery for an alleged assault involving three persons at the center on Sept. 7, state police said yesterday.

Lesti also was punched in the stomach during the fracas, his mother said. Two other residents, Stuart Leby and Joseph Wood, were also assaulted in the attack, state police said.

The Sept. 7 incident is the second time in two months that a Great Oaks employe has been accused of mistreating patients. Zelma Butler, 30, of Capitol Heights was charged Aug. 29 with assault and battery for allegedly slapping a mentally retarded woman resident in the face, Prince George's County court records show.

Spokesmen from the Maryland Department of Health and Mental Hygiene said yesterday that the two charges raise the number of alleged incidents of abuse by staff members this year to 21, a figure that is smaller than in previous years.

In the last 12 months, a total of 176 instances of alleged improprieties by employes have been reported.

Of the earlier 19 cases involving allegations of patient abuse, five have been found to be warranted, spokesmen said.

State officials are expected to release a statement this week concerning conditions at Great Oaks, the state's second largest institution for the mentally retarded.

A three-member inspection team from the health department, responding to complaints about the institution, visited the site Sept. 26 and 27 to interview employes and members of the administration.

State police said Lynn was charged with three counts of battery after another employe who saw him strike the residents reported the incident to a security guard at Great Oaks.

The security guard, following recently enacted law, was required to file a report with the state police.

Great Oaks personnel director Wayne Keegan said Lynn, a four-year employe, was suspended without pay. A hearing has been set for Nov. 29 at District Court in Hyattsville. Lynn could not be reached for comment.

Butler, a five-year employe, has been put on leave with pay pending an internal investigation. Her hearing date has been set for Nov. 5 in Hyattsville, records show. She could not be reached for comment.

Lesti, a 44-year-old single parent, said the situation frustrates her. "This is nothing compared to the other things that have happened to him. If I had all the money in the world, I wouldn't have him there.

"The only thing I can say is that they are short on money, short on staff. They have some very good people and they have some people who aren't trained at all to be there."