With Clint Eastwood starring as a veteran Secret Service agent in Wolfgang Petersen's crisply entertaining 1993 movie, the key question is who gets to play the implacable assassin sworn to drop the President. The choice was John Malkovich, who received a well-deserved Oscar nomination for his efforts in providing an insinuating, intrinsically adversarial presence, an ideal foil for Eastwood's bluntly straightforward delivery. Traumatized ever since the killing of J.F.K., Eastwood's Frank Horrigan wants to be on hand when Malkovich makes his try. Petersen brings many of the same qualities to the film as Eastwood himself would: a lean, unadorned style, a concern with pace and an understanding of genre. Petersen, best know for the splendid "Das Boot," is as good a match for Eastwood on his side of the camera as Malkovich is on his (Showtime Sunday at 8 p.m., Saturday at 8 p.m.).