`Tour of Duty' - weekly Vietnam drama. Despite seriousness of purpose, premi`ere is riddled with clich'es

Tour of Duty CBS, Thursday, 8-9 p.m. Premi`ere of new series. It's Vietnam in the 1960s, but the story is as old as war: young soldiers learning to depend on one another under the terrible stress of combat.

The fighting unit that this series will follow has the time-honored cross section of types - the the muscular California blond, the patriot, the protester, the Latino (``Man, I'm from the Bronx - blood is nothing new ...''). And it has Terence Knox as their war-wise sergeant, who pulls them all together with the kind of gutsy caring and inner fatalism some viewers will remember from World War II films. There's a reasonably convincing sense of the soldiers' grim initiation. Tension builds before the first real skirmish, and later battle scenes are horrific, capturing the chaos and randomness of warfare, yet keeping the players straight by showing us individual reactions.

In light of the early time slot, these sequences call for parental discretion in the case of younger children. Actually, there won't be many of them - too expensive. The word among advertising agencies is that they may occur only every four weeks or so.

When you see the helicopters moving over hilly terrain, it may remind you of ``M*A*S*H,'' but this series is not the Vietnam equivalent of that classic program with a Korean war setting. ``Tour'' lacks the jaunty survivalism of ``M*A*S*H.'' It plays its war straight, plunging into Vietnam with a decent seriousness of purpose - and with clich'es flying: the presumably dead enemy who inches unseen toward a gun and shoots; the protester who stabs him and mutters, ``I killed him,'' incredulous at his own instincts; the soldier who goes berserk under fire.

``Tour'' could have used a few quieter moments of foxhole introspection, a savoring of the specific atmosphere. Maybe this is too much to expect within a series format, or maybe it will come later, during those less expensive nonbattle sequences that promise to dominate. But I suspect many Vietnam vets will say the show doesn't evoke the special feel of what they experienced. Even people who've never been near the place may say the program takes a typically shallow TV-series approach to a complex subject.

Yet at least it deals with the subject of Vietnam, without brilliance, perhaps, but thus far without affectation, either.