BIRDY--He loves birds, and now that wartime combat has shocked him into insanity, he retreats from the world in an all-consuming fantasy of being one. Desperate to help, his best friend spends long hours with him, recalling their boyhood adventures and looking for a key to his condition. An offbeat story, sincerely acted but heavily directed by Alan Parker. (Rated R) KING DAVID--The biblical account of David has great movie possibilities, but this overblown production smothers them with wooden performances, leaden filmmaking, and a screenplay that can't get the story straight. Hard to believe this thudding drama was directed by Bruce Beresford, who gave us the poetic ``Tender Mercies'' not long ago. (Rated PG-13) LOST IN AMERICA--An advertising man and his wife ``drop out of society'' in search of meaning and adventure, and their quest is hopeless from the start. A tough, eccentric, very funny comedy from Albert Brooks. (Rated R) A PRIVATE FUNCTION--World War II has just ended, rationing is in full swing, and a nicely laid table has become England's biggest status symbol. Goaded by these circumstances, our henpecked hero steals a pig but has too much heart to slaughter it. There are a few laughs to be gleaned from this mild comedy, starring Michael Palin and Maggie Smith and directed by Malcolm Mowbray. (Rated R) THE SLUGGER'S WIFE--Neil Simon's latest is a one-joke comedy with serious overtones; it's about a baseball star who can't hit when his spouse isn't there to cheer him on. Rebecca de Mornay has some strong moments as the wife who dreams of her own singing career, and the supporting cast is likable. But the real fun is watching the zany, anything-goes directing style of Hal Ashby run circles around the pinched, Simonized screenplay. (Rated PG-13) THE WILD DUCK--Someone snipped Henrik Ibsen's play into little pieces and glued them back together, losing a lot of them along the way. You can still follow the plot about interlocking secrets of two families, one poor and one rich, but the action is hectic and discombobulated. Among the casualties are a fierce and funny performance by Jeremy Irons and a brooding one by Arthur Dignam. Australian filmmaker Henri Safran directed. (Not rated) RATINGS: R -- May contain violence, vulgar language, sex scenes, and nudity. PG13 -- May contain vulgarity and sex scenes.