Senator Clinton’s Republican challenger, John Spencer, said yesterday that the New York senator would make a “tremendous” candidate for president in 2008, but criticized her stance on Iraq, votes against tax cuts, and the rest of her record in Congress.

Mr. Spencer, the former mayor of Yonkers, used his airtime in the second and final Senate debate to cast Mrs. Clinton as an opportunist using the Senate as a springboard to the White House. Mrs. Clinton defended her position on Iraq, discussed Iran and North Korea, attacked Mr. Spencer’s record as mayor, and even aligned herself with prominent Republicans during the hour-long exchange on WABC.

Mr. Spencer, a conservative who opposes gay marriage and abortion, said: “Senator Clinton, I believe, and I’m trying to be a gentleman here, is being disingenuous with the people of New York State.”

He later softened his tone in responding to a question about a Time magazine cover story that offered two choices on Mrs. Clinton — Love Her or Hate Her. “The word hate is not a good word,” he said. “You know I happen to like Hillary Clinton.”

Mrs. Clinton — who opinion polls predict will win re-election in a landslide — maintained that she’s “made no decision” about running for president in 2008. She refused a pledge to keep her job in the Senate for the next six years and said voters who are concerned about that should “factor that into their decision.”

In defending her vote for the war in Iraq, Mrs. Clinton said, “If we knew then what we now know there would never have been a vote and there would never have been a war.” She also said Iraq needs to take over more of its own security.

“I’m not one who believes in do-overs in life,” she said. “You know I made the best judgment that I could make at the time. I regret deeply the way the president and his advisers used the authority Congress gave him.”

Mrs. Clinton’s performance in the two debates over the weekend gave voters a taste of how she’ll frame herself as a candidate if she runs for president.

Yesterday her answers on national security and social issues seemed designed to burnish her credentials as an electable presidential candidate who could appeal to moderate voters — a demographic she is trying to win over in this election.

Her efforts were most evident when she touted her work with the Republican Majority Leader in the Senate, Bill Frist, on electronic medical records, and with the man who served as Republican leader in the House, Tom DeLay, on adoption services.

The dean of the public affairs school at Baruch College, David Birdsell, said Mrs. Clinton did a solid job. “One of her goals here is to rack up as many Independent and moderate Republican votes as she can,” Mr. Birdsell said. “John Spencer is a good person to do that against because he appeals to more rock-ribbed conservatives.”

A Vietnam veteran, Mr. Spencer shrugged off opposition to the war, saying America can’t leave Iraq until the country is stable.

Mrs. Clinton said Iran “cannot be allowed to obtain nuclear weapons” and that America should hold direct talks with Iran and keep “all options on the table.”

She defended the Clinton administration’s dealing with North Korea —which Senator McCain criticized earlier this month — saying the country did not obtain nuclear weapons in the 1990s. She criticized President Bush for leaving the regime with plutonium rather than keeping inspectors there.

The two candidates sparred on domestic issues as well. Mr. Spencer criticized Mrs. Clinton for changing her position on parental notification when it comes to minors having abortions. He also criticized her votes against Supreme Court judges John Roberts and Samuel Alito.

Mrs. Clinton denied that she had used the “litmus test” of abortion or any one issue in rejecting Messrs. Roberts and Alito.

After yesterday’s debate, the Spencer campaign sent reporters 10 emails touting his points. The Clinton camp, which has been largely focused on helping other Democrats win, did not send out any.