Fairfax County police officer Ray M. Clements interrupted his foot patrol near Holly Hill Road yesterday to wave to three passing Falls Church High School coeds. They looked back-- startled.

The teen-agers had just seen more than an a rare friendly gesture from a policeman. Following an announcement earlier in the day by Fairfax Police Chief Richard A. King, foot patrols have become department policy for a fraction of the county's 700-member force.

The program, which comes at a time of growing criticism of alleged police brutality, is intended to get officers out of their air-conditioned patrol cars and into closer contact with those they are paid to protect.

Between 1 and 9 p.m. each day, 50 of the shift's 80 officers will mix with residents on their beats under the "Community-Oriented Foot Patrols" that began this week. King wants each officer to devote at least an hour a day to pounding the pavement.

"This is a significant step," King said. "It will attempt to get officers and community members together on a non-adversary basis. In most cases, they don't talk unless a person is suspected of committing, or is a victim, of a crime."

King said the plan will increase police visibility, act as a crime deterrent and heighten a sense of security among residents. But King said he also hopes to develop better relations between Fairfax police and residents.

Relations between Fairfax County residents and the police have deteriorated after a series of incidents in which the police have been accused of using excessive force.

Last month, an Alexandria couple, their son and a stepson, were arrested and charged with assualt, resisting arrest and public drunkenness. They in turn said they were beaten and clubbed unnecessarily by two Fairfax County officers. The Alexandria residents face a court hearing on Oct. 12 while an internal police investigation of the incident continues.

In addition, Fairfax County police mistakenly killed two persons during the past year. The officers involved were cleared in internal investigations of wrongdoing.

Most officers interviewed yesterday were enthusiastic about the new patrols.

"We've been mainly confined to the cars until now," said Robert DeGroot, 25, who has been assigned a foot patrol in Hideaway Park off Route 66 near McLean. "I think it will be good, and I like being out with the people. But it will take some time for them to get used to it."

Fairfax Deputy Police Chief Carroll D. Buracker said some of the officers at each of the county's seven district stations eventually will be permanently assigned to patrol some subdivisions on foot. Others will do it on a rotating basis in each of the county's 52 patrol areas.

Kevin Pewtherer, a Holly Hill Road resident who heard Clement's blaring portable police radio over the din of his tractor lawn mower yesterday, said he thinks the foot patrols are an excellent idea.

"You need 'em through here." Pewtherer said. "The kids smoke too much dope, leave beer cans all over creation. Having a foot patrol will cut down on crime."