Ronald A. Crews, the former Georgia state lawmaker who has spearheaded the push to ban gay marriage in Massachusetts, has taken initial steps to run as a Republican for the congressional seat now held by US Representative James P. McGovern, a four-term Democrat, state officials said yesterday. On Thursday, Crews, who moved to Ashland roughly three years ago to head the Massachusetts Family Institute, pulled paperwork to gather signatures required to seek the GOP nomination, said a spokesman for Secretary of State William F. Galvin