Twenty-six Prince George's County jail guards who were fired for going on strike last summer have filed a $7 million suit against their union, charging that union officials told them it was legal to go on strike.

The 26 were among 37 guards who staged a walkout Aug. 12 that triggered a three-hour rampage by jail inmates. The disturbance was quelled when police, sheriff's deputies and state troopers stormed the building's second floor and regained control.

The 37 guards who staged the walkout were fired by County Executive Lawrence J. Hogan in September. The guards are currently contesting their dismissals in administrative hearings before the county personnel board.

The guards' suit, filed Friday in Prince George's County Circuit Court, alleges that the officials of the American Federation of State, County and Municipal Employees "conspired to commit actual fraud" on union members by "falsely representing" to the guards that a strike would be legal.

"The union violated a position of trust that the union has with its members," said the lawyer for the guards, Richard Cotter. "The union has a duty to represent its members in good faith, and it did not."

Paul Manner, the union official who was named in the suit, did not return phone calls yesterday.

According to the suit, Manner and lawyers for the union advised the guards that it was legal to go on strike although the county's public employes relations board had said in July that the planned strike would be illegal. After the guards went on strike and a circuit court judge issued a court order prohibiting them from continuing the strike, the suit charged. Manner still asserted it was legal to stay on strike, the suit alleged.

"This is a situation where Hogan and union officials were fighting," said one lawyer connected with the case. "There's an old African saying, 'when two elephants fight the grass gets trampled.'"

The suit asks for $2 million in compensatory damages and $5 million in punitive damages.