IT'S NO LONGER ask what you can do for your country. It's ask what your country can do for your screenplay. Tom Hanks and John Candy make war on the Peace Corps in "Volunteers," a belated lampoon of '60s altruism and the idealistic young Kumbayahoos who went off to save the Third World.

It's an on-again, off-again effort, with Hanks as an obnoxious preppie who joins the Corps to escape an angry New Haven bookie, and Candy cast as an irritatingly gung-ho engineer. The two try to recreate last year's big "Splash," but the comic chemistry just isn't there, especially for Candy, who's uncomfortable in a role that seems to have been written for John Belushi.

Besides that, bland, inexperienced costar Rita Wilson gets in their way as a nurse who tries to change Hanks' ways -- but in the end trades her conscience for a Coke in this jumbled, jeering screenplay by Ken Levine and David Issacs.

The story takes place in Southeast Asia, where the three are assigned to build a bridge over the River Thai, a project of interest to the local opium warlord, the Communist rebels and a creepy spook with the CIA. Matters are further complicated when the villagers refuse to do the work because it requires that they cut down their sacred teak trees.

There are plenty of laughs, but the white- man's-burden jokes and gibes at idealism make this an uncomfortable comedy. Hanks, falling in and out of a Cary Grant imitation, is usually left holding the bag with racist punchlines like: This is "regular five-card stud except deuces are wild for white men." He can also tell when his Thai sidekick is lying because his eyes get round. Usually they're slanted. Get it?

Actually the joke is on Hanks because his sidekick, Gedde Watanabe, steals the show. Watanabe, best known as the Chinese exchange student in ''Sixteen Candles," plays an English-speaking villager who is being amorously pursued by three gay sumo wrestlers who guard the local opium lord.

Watanabe rises above the demeaning role, declaring resignedly: "So I die before I have a woman. I built a bridge. Fat guys touched me. I've had a full life."

THE VOLUNTEERS (R) -- At area theaters.