Mayor Bloomberg, seeking to boost his Republican Party bona fides yesterday, announced that Rep. Vito Fossella, the congressman whose district includes Staten Island and parts of Brooklyn, will be the Republican chairman of Mr. Bloomberg’s 2005 re-election campaign.

“Vito learned about politics from the ground up,” Mr. Bloomberg said yesterday as he announced Mr. Fossella’s post. “He brings a lifetime of experience helping win Republican races in New York City to the table, and there is simply no other person I’d rather have in my corner or at the head of my campaign,” Mr. Bloomberg said.

Mr. Fossella, for his part, made it clear that he would work tirelessly to ensure Mr. Bloomberg gets another four years. “I look forward to helping tell this success story and working alongside the Mayor and his team to ensure his victory in November,” he said. While the congressman and the mayor have been discussing this year’s reelection campaign for some time, they only determined Mr. Fossella’s official role over a shared pizza last week, the mayor’s aides said.

After they both marched in the rainy St. Patrick’s Day Parade at Bay Ridge last Sunday, Messrs. Bloomberg and Fossella had a pizza together at Gino’s Restaurant on Fifth Avenue at Bay Ridge, where they made their political union official, they said.

The announcement of Mr. Fossella’s appointment came just a day after news leaked that the Bloomberg campaign has also been courting a high-ranking Republican in Governor Pataki’s office, John Haggerty Jr., head of legislative affairs. If Mr. Haggerty joins the Bloomberg team he would be the second Republican, after Mr. Fossella, hired as a key political aide to Mr. Bloomberg.