YEARNING for big-screen stardom, too many television actors make the fatal mistake of leaving a hit series in a bid for more fame and fortune, and the list of casualties is long. In recent years, one show has spawned an astonishing number of defectors: LA Law. Harry Hamlin, who played Michael Kuzak in LA Law, left the show several seasons ago to no avail. Two of his cinematic efforts, Murder So Sweet (1992, 20:20 Vision, 90 minutes) and Under Pressure (1992, 20:20 Vision, 94 minutes) have made it into video stores here, and while Hamlin acquits himself well enough, the films did not set Hollywood alight. In both, Hamlin plays a husband with murderous leanings. In Murder So Sweet, it is his string of failing marriages which pushes him over the edge. Finally, he reasons, if he kills his wives, they cannot leave him. But all attempts to warn his spouses - first, Faith Ford (of TV's Murphy Brown ) and then Daphne Ashbrook - fail. In Under Pressure, Hamlin vents his fury on the hospital where his wife had a tubal ligation, following her ninth pregnancy. Hamlin believes the sterilisation operation was both carried out against his wife's will and contravened God's commandments aboutgoing forth and multiplying. He is better in this disturbing, often chilling, portrayal of a man driven to the brink of insanity. Another LA Law defector not enjoying any better luck is Jimmy Smits (who played Victor Sifuentes). Despite a promising appearance in Switch with Ellen Barkin, he has since been reduced to appearing in Stephen King's Tommyknockers (1992, WEA, 115 minutes)as an alcoholic poet left to save his town from from space aliens, and Gross Misconduct (1992, PolyGram, 100 minutes) in which he is a professor accused of raping a student whose sexual advances he has been spurning. Another two LA Law stars who occasionally strike out on their own are husband and wife team Michael Tucker and Jill Eikenberry (who play Stewart Markowitz and Anne Kelsey, also married). They star in A Town Torn Apart (1992, Odyssey, 91 minutes) as teachers who incur the wrath of a town when they try to teach the children at a run-down, inner city school with methods not officially sanctioned by the authorities. While this offers solid performances, it is tiresome to see Tucker and Eikenberry do little more than reprise their LA Law roles. Videos from KPS.