Even though he said very little during his turn as the villain in Lethal Weapon IV, Hong Kong star Jet Li stole the show. His calm, assured presence and seemingly superhuman agility make most American action heroes look like muscle-bound wimps. His latest Hollywood flick, Romeo Must Die, works best when it capitalizes on Li's remarkable assets. He clobbers more bad guys with a firehose than Sylvester Stallone or Jean-Claude Van Damme can with loaded machine guns. Li uses his lethal skills in a routine story about a gang war between black and Chinese gangsters. The outcome of the battle is obvious because of silly red herrings, and Li's romance with a black don's daughter (moonlighting singer-model Aaliyah) is sadly anemic. The supporting cast is unusually strong, especially with Delroy Lindo (The Cider House Rules) as a thoughtful godfather and Isaiah Washington (True Crime) as his suave but ruthless enforcer. While the action is consistently rousing, one wishes the script were as energetic and galvanizing as its star is. (R)