Now public television has even mellowed out James Fenimore Cooper. What next? "The Leatherstocking Tales," four half-hour episodes derived from novels by Mark Twain's least favorite author, begin tonight on "Once Upon A Classic," at 7 on Channel 26 and other PBS stations.

Unlike most of the "Classic" offerings, this one was produced not in England but by Pittsburgh's WQED, and shot on location in western Pennsylvania. Writer John O'Toole did the adapting, calming Cooper down to a state of woodsy reverie that is neither unpleasant nor very compelling.

Cliff De Young, sounding a lot like Jack Nicholson occasionally crossed with a young John Wayne, makes a prudent and easygoing Natty Bumpo, and as friendly Delaware chief Chingachgook, Roger Hill has a considerable stoic charisma, even if he does look like a Manhattan Indian -- lower East Side, perhaps.

The spirit of Cooper, such as it is, has been preserved by O'Toole, who also delivers the requisite pro-social-telegrams. Young viewers will recognize the film's comments made on women's roles in frontier days; the Indians can think of no juicier insult than that a man might "cry like a weak woman" or "beg like a woman" when put to tests.

Director Nick Sgarro does nothing particularly wizardly with this material, and children's imaginations are probably more richly served by reruns of old Hollywood adventure spectacles; "Leatherstocking" has that very-PBS aura of ineffectual dimness. But in the first episode, the filmmakers show prowess at evoking the thrill of being lost in the woods or of sailing a canoe down an untamed river, and that counts for something.