A three-member panel of the Prince George's County Circuit Court yesterday ordered the county to reinstate about 30 jail guards who were fired in August 1980 when they went on strike.

County Attorney Thomas Smith said the panel found that the guards were illegally fired when they participated in an 11-day county employes' strike.

Yesterday's decision upheld, in part, a decision made by Circuit Court Judge James M. Rea last December.

But the panel found that Rea exceeded his authority when he ordered the county to give the guards back pay, Smith said.

The panel said the back pay issue must be decided by the county personnel board. Smith said the guards' back pay would cost $1.6 million.

"We're very pleased with the decision," Smith said, adding that he expected the guards to return to work as soon as possible.

"I think that it the panel's decision was substantially correct and justified as far as it went," said attorney Leonard Goldstein, who represents most of the jail guards.

Goldstein said he believes the guards are entitled to back pay.

The guards were fired in 1980 by former County Executive Lawrence J. Hogan after they marked the start of the county's first employe strike by walking off the job at the County Detention Center in Upper Marlboro.