Fairfax County Police Chief Richard A. King said yesterday he is following a recommendation that the county's prosecutor says could have saved the life of a man mistakenly killed Dec. 29 by police.

King said he is ordering officers assigned to stakeouts inside buildings to be in uniform, an action that Fairfax Commonweatlh's Attorney Robert F. Horan recommended following the accidental shooting of a school custodian.

The custodian, John Jackson, was killed by an officer in civilian clothes, David Lubas, when Jackson entered the Talent House School with his own gun to begin his own stakout there. Jackson went to the private school, unaware that Fairfax police also had a robbery stakeout there, police have said.

"There is no doubt in my mind if Jackson had seen a [police] uniform, he would have never raised his gun," Horan said yesterday. When Jackson raised his gun, he was shot three times by Lubas, police have said.

The chief said the county has had a policy of making uniforms optional on stakeouts although a uniformed officer is required to be with officers serving search warrants. Officers assigned to what police called "external" stakeouts will not be required to wear uniforms because they would be "too conspicuous," King said.