In terms of an acting disguise, Mandy (The Princess Bride) Patinkin beats all his competitors. In this futuristic thriller, Patinkin plays a cop from outer space. Sure he looks weird. But guess what? Even with his face covered in rubber, Patinkin manages to fashion a character of warmth, humor and dignity. He's wonderfully impressive. The movie itself is something of a mess, though a diverting one. The time is 1991. The place is Los Angeles, where 300,000 of Patinkin's humanoid race have recently immigrated. Now they must be integrated into human society. The idea behind Rockne S. O'Bannon's script is provocative: Use these aliens to make us see racial prejudice in a new light. But it's an idea O'Bannon and director Graham (The Final Conflict) Baker neglect to develop. Action takes precedence. It's Lethal Weapon in latex as Patinkin teams up with bigoted human cop James Caan to stop the import of drugs from another planet. Caan calls Patinkin a slag, their police car is changed by a jokester to read "E.T.P.D." and, natch, the partners learn to appreciate each other by acting macho. Oh, for the movie that might have been. Still, what remains is pulse-pounding fun. (R)