Tom Hicks has been giving out a lot of guarantees lately. In November Hicks, trying to raise money for a new fund, had to take the unusual step of having his LBO firm assure investors a 20 percent annual return. Last month Hicks, who owns the Texas Rangers in addition to being chairman of Hicks, Muse, Tate & Furst, shocked the baseball world by inking all-star free agent Alex Rodriguez to a record ten-year, $252 million contract. Hicks had better hope that A-Rod performs better than some of his firm's recent investments. A leading financier of fledgling technology companies, Hicks Muse saw several of the start-ups it bankrolled falter badly last year. One, ICG Communications, a telecommunications company that sells Internet and telephone services to businesses, into which Hicks Muse had poured $230 million in February, declared bankruptcy in November. Hicks is optimistic about the prospects for his new, 25-year-old shortstop, who last season swatted 41 home runs and drove in 132 runs while batting .316 and is seen as a sure future Hall of Famer. Hicks, who endured boos the day the contract was announced from critics who deplore baseball's version of irrational exuberance, predicts that Rodriguez will one day break Hank Aaron's career home-run record. "I,m a hero in Texas," says Hicks, who bought the Rangers two years ago for a mere $250 million. "But people are questioning my sanity in New York."