In the land of criminals, the criminal-at- large is a hero. Such is the assumption of "The Pursuit of D.B. Cooper," which extends into merry fiction the known exploits of a man who, assuming that name, hijacked a plane in 1971 and then parachuted to the ground, where his trail has been lost.

The film portrays an America in which every person in every remote corner of the landscape -- the trailer-park housewife, the last-chance gas-station attendant, the old man who just hangs around -- is audaciously crooked. Small wonder, then, that The Jolly Hijacker should be a national idol.

But whatever the extent is of American admiration of outlaws in general and this one in particular, and of the attitude that crime against large businesses is somehow victimless, it's amusing to see how the film justifies its premise. It does so by endowing its hero with all the attributes of virtue, wholesomeness and morality.

Compared to Treat Williams' shamelessly aw-shucks performance as Cooper, Superman looks like a wily sneak. Our hero loves the outdoors, wouldn't hurt a fly, is sensitive to other people's feelings, adores his wife, respects his father, excels in sports and obviously sees his dentist twice a year. Aside from that small matter of the $200,000 robbery, he is also scrupulous about money -- pinning bundles of it to a tree, for example, in payment for grabbing someone's horses for a getaway.

One may well ask why he needs to get away, as everyone seems to be on his side; and indeed, the job of representing the legal side of things in this picture is a thankless one. The formidable Robert Duvall undertakes it with amazing good humor, playing an agent of the insurance company as such a sporting guy, too, that the persecution of the all-American hijacker is bearable because it is viewed as fair, if madcap, outdoor sport. And as the heartless insurance company also persecutes its own agent, and as that agent clearly acts outside of the law for ulterior reasons of his own, his integrity, within the terms of the film, has been protected.

Moral questions aside, this is a chase picture, slightly fresher-looking than the ordinary highway version. There are chases on whitewater rapids, on horseback and between a car and an airplane. Each one involves a capture and an escape for a subsequent chase, so it's a little less exciting as the pattern becomes clear. But no one gets hurt, our prankster being too considerate for that, and it's all done to folk music.

THE PURSUIT OF D.B. COOPER -- Opens this Friday at the Uptown.