EXETER, N.H. — It had the outlines of a significant event: A three-term governor of New York, who forced Mario M. Cuomo from office and led his state through the Sept. 11 terrorist attacks, announced Thursday that he was running for president.

But as the former governor, George E. Pataki, prepared in recent weeks to announce his candidacy, he conceded to friends and allies that he was an extreme long shot for the Republican nomination. Once a formidable figure in the party, Mr. Pataki has entertained campaigns for the presidency numerous times over the years, seemingly waiting for the perfect moment — only to jump in now, when his profile has waned.

Mr. Pataki declared his candidacy late Thursday morning in an address to supporters in New Hampshire. He vowed to enact far-ranging changes in Washington, pointing to his record of attacking government spending and entrenched Democratic interests.