The Justice Department, which filed a hiring discrimination suit against the Prince George's County Police Department three years ago, is seeking its dismissal because of a sharp increase in minority recruiting.

The request, made by both the Justice Department and the county government, was submitted to U.S. District Court Judge Joseph H. Young in Baltimore this week. It came a year after the department said it would drop the suit if the county continued its minority recruiting efforts.

Although only 9 percent of the county's 859-member police force is black, half of the latest class of 24 recruits are black.

A quarter or more of the county population is black, according to recent estimates.

The dismissal motion reflects Prince George's County's "good faith effort to increase minority representation at entry-level ranks," said County Attorney Robert Ostrom. He maintained, however, that the police department's efforts to recruit minorities and women were not a result of the suit.

"That effort was under way before the suit happened," said Laney Hester, president of the Fraternal Order of Police, the policemen's union.

But Justice Department officials have pointed to figures showing a steep rise in minority recruiting since the suit was filed.

"Between 1972 and 1974, four percent of the police recruits were black; between 1974 and 1976, 15 percent were blacks or women; since the lawsuits was filed in 1976, 40 percent of the recruits have been blacks or women," Justice Department lawyer Maimon Schwartzchild said last year.

Hester said gains have been slow because the new recruit class is the department's first in 30 months.

Police recruit applicants must pass a written test and a physical examination. They then appear before an interviewing board, a session that Hester says weighs heavily on selection.

Hester said yesterday that blacks already on the force have been helping recruit more blacks. "We've been stealing policemen from other departments," he said, adding that black policemen had been lured away from D.C., Baltimore City and Maryland state police forces.

Last year, county police Col. Vincent duCellier, administrative and personnel officer, said recruiters had been contacting placement officers at military installations and black colleges as far away as California in an effort to bring more blacks into the department.

"But most important, we took efforts to make minorities know we really wanted them. If they needed temporary housing, we arranged it. If they needed temporary transportation, we provided it."

DuCellier could not be reached for comment yesterday.