The former mayor, in an extended interview with The Post, also predicted that Gov. Paterson’s high-profile effort to legalize gay marriage would anger many New Yorkers and spark a revolt that could help sweep Republicans into office in 2010. “This will create a grass-roots movement. This is the kind of issue that, in many ways, is somewhat beyond politics,” said Giuliani, a two-term mayor who unsuccessfully sought the GOP presidential nomination last year.