Mayor Bloomberg’s girlfriend, Diana Taylor, is crossing party lines to support Democratic congressional hopeful Sean Patrick Maloney — who is trying to unseat Republican freshman Congresswoman Nan Hayworth to represent Rockland and Westchester counties.

Taylor, a registered Republican, will host an Oct. 11 fund-raiser for Maloney at the mayor’s Upper East Side home, according to an e-mail his campaign-finance director sent out yesterday.

Maloney, a gay congressional candidate, is locked in a tight race against Hayworth.

“I don’t support parties per se. I support people,” Taylor told The Post. “I support Sean because I think he is the best candidate for the seat and he will do the best job for his district, for the state and for the country.”