HALF LIFE - Provocative documentary on American nuclear testing in the Marshall Islands, charging that great harm has been wrought on many of the inhabitants there. Thoughtfully crafted by Australian director Dennis O'Rourke. (Not rated) HEARTBREAK RIDGE - A crusty Marine whips a young platoon into shape, shows that the ``old'' methods are better than the ``modern'' ones, and then rescues Granada with a little help from his friends. The shoot-'em-up climax is preceded by almost two hours of numbingly repetitious brawls and obscenities. But there's a sad anthropological interest in the constant anatomical and homoerotic humor, which betrays a grim insecurity beneath all the macho strutting and bone-crunching. In addition to playing the hero, Clint Eastwood directed the sorry show. (Rated R) THE MOSQUITO COAST - Convinced that the United States is on the verge of self-destruction, a brilliant but obsessive individualist moves his family to Central America's treacherous wilds. There he tries to conquer the overwhelming forces of nature and build a new community based on hard work, ingenuity, and a few demented notions all his own, including the idea that ice is nature's most precious gift. The capable efforts of director Peter Weir and screenwriter Paul Schrader don't quite reproduce the manic intensity of Paul Theroux's original novel. Ditto for Harrison Ford's performance, although like the filmmakers, he comes thrillingly close at times. (Rated PG) STAR TREK IV: THE VOYAGE HOME - If this keeps up, we'll have more Trekkie film sequels than original TV episodes. And that's fine if they're all as charming as this one. The crew members of the spaceship Enterprise time-travel to 1986 in search of some humpbacked whales, which they need to solve a 23rd-century crisis. Like interstellar cousins of Crocodile Dundee, they hilariously grope their way through today's San Francisco, finding each aspect of the '80s urban scene more inexplicable than the last. In comparison with a ``Star Wars'' or Indiana Jones hit, the visual humor is refreshingly gentle and the dialogue is witty, wistful, and even wise at times. Leonard Nimoy, who plays his perennial role of Spock with ease and assurance, also directed this unexpected treat. (Rated PG) NUTCRACKER - Lively rendition of the classic Tchaikovsky ballet, with an unusually large amount of plot material from E.T.A. Hoffmann's original story to stitch the dances together. Carroll Ballard directed the movie, which was designed by Maurice Sendak and choreographed by Kent Stowell, whose Pacific Northwest Ballet is the collective star of the show. While the production sets no high new standards for the dance-film genre, it's always perky and sometimes very inventive. (Rated G) EVERY TIME WE SAY GOODBYE - During the 1940s, an American gentile in Israel falls in love with a young woman from a very traditional Jewish family. Their story, directed by Moshe Mizrahi, is sweet but sappy. (Rated PG-13) RATINGS: Films with ratings other than G may contain varying degrees of vulgar language, nudity, sex, and violence.