"Deliverance" director John Boorman gets back to nature in "The Emerald Forest," a ludicrous loincloth adventure based on fact. Son Charley Boorman joins him as a modern-day Greystoke in his overblown, didactic film, a crusade to save the Brazilian rain forests which are disappearing, but not so quickly I bet as this film.

The real story concerned a Peruvian engineer, but here an American dam builder's son is spirited away by Amazon Indians. When his father (Powers Boothe) finds him 10 years later, 10,000 years of progress have come between them. Tomme, as he is now called, is a Stone Age warrior, son of the chief and future leader of the tribe.

"You are Da-dee," says the boy after rescuing his father from neighboring cannibals who have already had a French journalist for an hors d'oeuvre. Tomme's spiritual father (wizened, wonderful Rui Polonah) heals Da-dee by placing hot coals on his clavicle. Later the chief urges the father to stay in the pleasant village, far from the dead world of the Termite People who chew up trees and dam the rivers.

And the members of tribe are gorgeous. Boorman, obsessed with the beauty of his son, lets the camera linger on the boy, decorated with blue-green tattoos and feathers to match his eyes. It's like baby pictures gone too far. Nubile nymphets, enough to fill the Trevi Fountain, lounge in waterfalls. And the tribal people dance about like conventioneers at a Honolulu Hyatt luau. In fact, the whole movie seems more Polynesian than Brazilian.

Da-dee does stay for Tomme's wedding in which the lad knocks his bride unconscious with a large club. But then progress encroaches on these sweet people, diminishing them, just as it nibbles away at the forests each day. Forty percent of the world's oxygen is produced here, declares the unfortunate aforementioned Frenchman (a hideous character, by the way). Screenwriter Rospo Pallenberg has not penned subtle stuff. But if you still don't get the point, Boorman adds a final warning, as if his movie were a cigarette pack.

He means well, but it all looks like the floor show at the Tiki Hut after you've had one too many pu-pu platters.

THE EMERALD FOREST (R) -- At area theaters.