They're double agents without a sneaking suspicion of their assignment. But if it has anything to do with comedy, it's sure to be "mission accomplished" for Saturday Night Live alumni Chevy Chase and Dan Aykroyd, romping through their first movie together: Spies Like Us. As two government desk jockeys who cheat their way through a civil-service entry exam and (incredibly) become globetrotting undercover operatives, Aykroyd and Chase generate the verve and spontaneity of a Bob Hope/Bing Crosby road movie. (Indeed, Hope turns up in a cameo, golf club in hand.) Top Secret. Eyes Only. And laughter assured.