A federal jury in Alexandria awarded a former Fairfax County employe yesterday $12,000 after finding that he had been defamed by another county employe. The jury also found the former employe had not been a victim of racial discrimination on the job.

The mixed verdict, which included $8,000 in punitive damages, came at the close of a two-day trial in which Gary Riviere, a former employe of Fairfax County's Department of Extension and Continuing Education, had sued the county and three of its employes for $360,000 for alleged racial discrimination and defamation.

"It appears to me the jury blamed one guy . . . for everything," said Riviere's attorney, David H. Williams. "I was surprised. I don't agree with that verdict."

Fairfax Assistant County Attorney Edward Rose, who represented the county and its employes, Robert J. Doyle, Rajandra N. Waghray and G. Stewart Bunn, declined to comment.

Riviere, 35, who is black, resigned from his job as an "extension agent" in July 1985 after being told he would be fired, according to evidence. He had been assigned to the county's gypsy moth control program.

Mark Greenleaf, an environmental control specialist with the District of Columbia government, testified that Bunn told him Riviere was fired because he had been apprehended for driving a county vehicle while under the influence of drugs or alcohol.

Bunn, who has since left the county's employ, testified he did not make that remark to Greenleaf.

Riviere denied any such incident and no evidence was presented during the trial indicating Riviere had been arrested for driving under the influence. Riviere testified the defamatory statement was widely circulated, hampering his ability to find another job in his field.

Riviere testified that in Fairfax he was told to wear a necktie during field work, assigned menial tasks that should have been shared by all employes, given conflicting instructions on how to perform his job and severely criticized for minor mistakes.

Waghray, who had been one of Riviere's superiors, denied these allegations and testified that Riviere had shown a lack of initative and poor performance on the job. He testified that he had asked Riviere to wear a necktie when he was addressing public groups.