WASHINGTON - Rep. Vito Fossella, citing "personal mistakes" after a drunken-driving arrest and disclosure that he fathered a child in an extramarital affair, yesterday became the 26th Republican congressman to retire rather than face re-election this year.

The New Yorker's exit comes at a bad time for the Republicans, but staying could have made things worse. A socially conservative incumbent in a socially conservative party, the congressman's personal baggage threatened to further weaken a listing GOP ship.

"This choice was an extremely difficult one, balanced between my dedication to service to our great nation and the need to concentrate on healing the wounds that I have caused to my wife and family," Fossella said in a statement on his congressional Web site, saying that he would serve out his term, which expires next Jan. 3.

The 43-year-old Republican has acknowledged fathering a daughter with a Virginia woman, Laura Fay. The two met while she was an Air Force officer working with Congress. He also has a wife and three children.

The lone GOP congressman in New York City, Fossella represents Staten Island and part of Brooklyn.

His departure puts more pressure on Republicans to hold the seat in November.

Republican Party officials have already begun searching for a successor.

The district "will vote true to its form in November and will send a Republican representative back to Congress," said Rep. Tom Cole of Oklahoma, who heads the National Republican Campaign Committee. He said that the committee will be "working quickly" to sign up a Republican contender. *