ST. LOUIS — Under intense scrutiny, Republican vice presidential candidate Sarah Palin stood her ground Thursday night against a vastly more experienced Joe Biden, debating the economy, energy and global warming, then challenging him on Iraq, "especially with your son in the National Guard."

The Alaska governor also noted that Biden had once said Democratic presidential candidate Barack Obama wasn't ready to be commander in chief, "and I know again that you opposed the move that he made to try to cut off funding for the troops and I respect you for that."

Biden responded that John McCain, too, had voted against funding, and said the Republican presidential candidate had been "dead wrong on the fundamental issues relating to the conduct of the war."

The clash over Iraq was the most personal, and pointed, of the 90-minute debate in which Palin repeatedly cast herself as a non-Washington politician, part of a "team of mavericks" that was ready to bring change to a country demanding it.

From the opening moments of the debate, Biden sought to make McCain out as a straight-ahead successor to an unpopular President Bush. "He voted four out of five times for George Bush's budget, which put us a half-trillion dollars in debt and over $4 trillion in debt since he got here," he said of McCain.

Palin merely accused Biden of reciting the past rather than looking to the future. "Americans are cravin' that straight talk" that McCain offers, she said.

The two running mates debated for 90 minutes on a stage at Washington University, their only encounter of a campaign with little more than one month to go.

Recent polls show Obama with a small but perceptible lead, and Republican officials said earlier in the day that McCain had decided to pull out of Michigan, conceding the state to the Democrats. At the same time, his own aides said the campaign may soon begin to advertise in Indiana — a state that has voted Republican in every presidential election since 1968.

Palin faced enormous challenges of her own, though. After five weeks as McCain's ticket-mate, her poll ratings had begun dropping and even some conservatives have questioned her readiness for high public office.

Her solo campaign events are few, and she has drawn ridicule for some of her answers in the few interviews she has granted — including her claim that Alaska's proximity to Russia gives her an insight into foreign policy.