The election of the century,"" and MacIlwain Evans, 26, not only backs fiery Tom Jeff Shadwell for governor of Virginia, he's for him heart and soul. Mac has much to recoup in a Shadwell victory. His father had to leave Virginia politics 20 years ago, under a cloud, and take a diplomatic post in South America. Big brother Lester had already made lieutenant governor and was a shoo-in for top job--when he died of a brain tumor early on in his term. Mac, in fact, is such a monomaniac about helping Shadwell carry the liberal Democrats into office that when he gets the first warm woman of his life into bed (she's from out of state), he's left speechless for lack of nonpolitical chitchat. Then, slowly, life and incumbent demagogue Miles Brock (""Godzilla"") take Mac to pieces, like a fileted shad. The very air turns weird as back runner Brock opens up a campaign of lies, slander, and vilification against Shadwell. And when Tom Jeff, the sure favorite, loses by a slim 11,000 votes, Mac finds that his real education is just begun. Sensitive characterizations, smoky rooms and deals, obsessive campaigning--a familiar story but told with a touch of Virginia class.