AUSTIN, Texas — Barack Obama and Hillary Rodham Clinton sharpened their differences on Iraq and healthcare last night but created the most sparks over their respective philosophies about how to bring about change.

Both had strong, even performances, but neither scored or floundered in any substantial way, meaning that the dynamic of Clinton attempting to stymie Obama's February momentum persists. He has won 11 contests since Feb. 5.

In the first of two debates before the next round of crucial primaries in Texas and Ohio on March 4, Clinton tried to drive home differences on their respective health insurance plans. Obama tried to portray Clinton as having flawed judgment on the war in Iraq.

But it was a question about Clinton's campaign assertions that she is ready to be president "from day one" that produced the sharpest exchange. By implication, Clinton is saying that Obama is not ready for the job and that his appeal is long on rhetoric and short on policy and accomplishment.

"I do think that words are important and words matter, but actions speak louder than words," Clinton said. A large crowd at the University of Texas Recreational Sports Center booed her, however, when she criticized Obama for borrowing a passage about the power of words from Massachusetts Gov. Deval Patrick, an Obama supporter.

She said that "lifting whole passages ... is not change you can believe in, it is change you can Xerox," mocking a central line from Obama's campaign.

In one of his strongest moments, Obama played off the boos by describing Clinton's attack as evidence "the silly season in politics" had arrived and arguing that voters wanted solutions, not divisive politics of the past evidenced in Clinton's attack.

"The notion that I plagiarized from someone who is one of my national co-chairs who gave me the line and suggested that I use it I think is silly," he said. "What I have been talking about is not just hope, not just inspiration, it is a $4,000 tuition credit" and specific ideas on healthcare, ending the war and other issues, Obama said.

He said that Clinton "has a fine record and I don't want to denigrate that record. I do think there is a fundamental difference between us in how change comes about."

Obama drew the sharpest line on the war in Iraq, saying that Clinton's vote to go to war in 2002 showed a lapse in judgment that would prevent her from drawing distinctions with likely Republican nominee John McCain in the November election.

The two also disagreed on Cuba, with Obama saying he would meet with new President Raul Castro without precondition. Clinton said that while she would entertain fresh diplomatic contacts, offering a presidential visit without preconditions "undermines" the ability of the United States "to take the measure of a man like Raul Castro."

Clinton's strongest moment was her final answer. She said she has been challenged in her life but realizes that "the hits I've taken in life are nothing compared to what goes on every single day in the lives of people across our country. And I resolved at a very young age that I'd been blessed and that I was called by my faith and by my upbringing to do what I could to give others the same opportunities and blessings that I took for granted."

The debate came on a day that a new poll showed Obama and Clinton in a virtual tie in Texas, reflecting a significant surge for the Illinois senator. He had been trailing by double digits in polls here before he went on a run of victories since Super Tuesday. The Washington Post-ABC poll released yesterday had Clinton at 48 percent in Texas, and Obama at 47. In Ohio, she led Obama by 50-43.