In a ruling issued yesterday, a Baltimore Circuit Court judge backed the city Police Department's decision to fire a lieutenant who was caught at an underground strip show while on duty last year.

Lawyers for Lt. John Mack had appealed the decision of a departmental trial board, which found the lieutenant guilty of 38 misconduct charges and urged his firing in October.

Police Commissioner Edward T. Norris, who earlier had told a City Council hearing that Mack was in a "whorehouse on duty," fired the officer.

Mack's lawyers had argued that Norris tainted the trial board by publicly announcing that the officer should be fired. But Judge Thomas E. Noel upheld the board's action.