"Air America" would like to be the "M*A*S*H" or "Catch-22" of the Vietnam War, but, despite the different backdrop, this is merely another clunky buddy picture.

You might not consider this a "different" backdrop, since there have been so many Vietnam movies in recent years, but "Air America" is a rare commodity — a Vietnam comedy.

Actually, the film is set in Laos, where the CIA is illegally running a secret airline that drops hundreds of boxes of supplies and weapons each day to "friendlies," those Laotian villagers in need of aid and soldiers battling the North Vietnamese at the border.

Of course, the CIA chief overseeing the operation is also involved in the dirty business of making and distributing heroin, in partnership with a corrupt Laotian colonel.

All of this may seem like dubious material for comedy, but if it were handled as dark satire with an edge, as were "M*A*S*H" and"Catch-22," it might have some snap. Instead this is happy-go-lucky, light comedy, which seems jarringly out of place in this setting.

Despite his top billing, Mel Gibson is not really the central focus of most of "Air America." Instead it is Robert Downey Jr., who has the nominal lead as an L.A. kid who's been flying a traffic helicopter for a rock 'n' roll station, circa 1969.

Downey is recruited by the CIA to join up with this band of misfits, as Gibson and his fellow thrill-seeking pilots spend their days air-dropping everything from rice and live pigs to rifles and hand grenades, while booze and local prostitutes provide their only diversions after hours. (One of the pilots has also built a homemade miniature golf course, complete with windmill.)

It's not the life of excitement Downey expected, of course, but there's a worse problem. As a naive young man with a highly developed sense of moral ethics, Downey is naturally repulsed by what he's involved in — especially when he discovers the drug angle.

Meanwhile, Gibson, who is married to a Laotian woman and has two kids, is a bit more self-involved. All he wants to do is continue to stash weapons to sell for his eventual retirement.

It's obvious that he lost his conscience some time ago. And it's just as obvious that Downey will start him thinking about things again.

Despite a few obligatory deaths, shootouts and plane crashes, there's never a real sense of danger or excitement here. And there are even fewer genuine laughs.

Authority figures are bigots and jerks, and religious faith takes it on the chin in the form of a nincompoop senator who tells everyone his life changed when he "found the Lord."

Gibson and Downey are appealing actors and they try their best, but the entire movie is on their shoulders. And the script, by John Eskow ("Pink Cadillac") and Richard Rush (director of "The Stunt Man"), is just too insipid for them to pull it off.

Director Roger Spottiswoode, who also gave us "Turner & Hooch," along with the more memorable "Under Fire" and "Shoot to Kill," seems to have simply thrown "Air America" together. The action sequences are workable, but dialogue exchanges and plot-driven scenes are a mess.

What's more, the lone significant female presence, Nancy Travis, seems to have had all her scenes left on the cutting-room floor, despite having third billing.

"Air America," rated R for language and violence, is a real mess. This one is strictly for die-hard Mel Gibson fanatics and fliers who will go see anything with a plane in it.