Jonathan Tasini, a labor advocate and former president of the National Writers' Union, announced a campaign Tuesday to challenge Hillary Rodham Clinton for the Democratic nomination for Senate, saying her vote to authorize the war in Iraq proves she is out of step with New Yorkers.

"People who supported the decision to go to war must be held accountable -- and that includes my opponent," Tasini said. "The war in Iraq was a war of choice, not a war of necessity."

Clinton, a member of the Senate Armed Services Committee, voted in 2002 for the congressional resolution authorizing President Bush to use military force in Iraq. Clinton has supported troop-level expansions even while criticizing Bush's handling of the war.

Tasini is Clinton's second anti-war challenger. A former Green Party member, Steve Greenfield, announced earlier that he would run against her for the Democratic nomination because of her refusal to call for an immediate withdrawal of troops from Iraq.

Asked about her challengers at an event in Schenectady, Clinton said, "I have no argument with anyone who wants to run for any office. That's what makes this such a great country and why I'm so hopeful that the Iraqi people will have the same experience."

Tasini said that the more than $250 billion that has been spent on the war could have been spent on health care, schools and "job opportunities for many Americans trying to pay their bills."

Clinton is up for re-election next year and leads national polls of the party's potential 2008 presidential candidates.

Polls show her beating Westchester District Attorney Jeanine Pirro or any other GOP challenger by a wide margin, and Tasini and Greenfield will face an uphill fight even getting on the primary ballot.

Tasini led the National Writers' Union, a freelancers' union affiliated with the United Auto Workers, from 1990 to 2003. He was the lead plaintiff in Tasini vs. The New York Times, an electronic rights case in which freelancers sued the Times and other media corporations over publishing rights. The case reached the U.S. Supreme Court in 2001 and was decided in favor of the plaintiffs.

Tasini is currently president of the Economic Future Group, a national consulting group. He is the author of two books: "The Edifice Complex: Rebuilding the American Labor Movement to Face the Global Economy" and "They Get Cake, We Eat Crumbs: The Real Story Behind Today's Unfair Economy."

A handful of supporters attended his campaign announcement at the W Hotel in Manhattan.