ST. LOUIS - Vice presidential candidates Sarah Palin and Joe Biden spent most of their time defending or attacking the two men at the top of their tickets, John McCain and Barack Obama, in a 90-minute debate Thursday night touted as a potential game-changer.

Whether the Biden-Palin confrontation will live up to its billing as the most consequential vice presidential debate in history may not be known for days, when analysts and public opinion polls weigh in.

Immediately after the debate, aides and activists in both camps praised their candidate's performance. Observers agreed that both avoided the kind of major gaffe that can send approval ratings plummeting.

Palin, the Republican governor of Alaska, repeatedly emphasized McCain's promise to keep most of the current federal income tax breaks in place, while challenging Obama's promise to raise taxes only on people who earn more than $250,000 a year.

Palin said Obama would end up hiking taxes on far more Americans.

Biden, a veteran U.S. senator from Delaware and a Democrat, defended Obama's tax proposals while hammering at McCain's plan to tax employer-provided health insurance and give families an annual $5,000 tax credit to buy their own coverage.

Biden said McCain's health insurance plan amounted to a tax increase on many Americans and would leave millions of them without insurance coverage. Palin disagreed.

Such back and forth continued when it came to addressing the rising cost of oil and gasoline, the war in Iraq and foreign policy troubles, particularly the threats caused by weak or belligerent governments in Iraq, Pakistan and Afghanistan.

Only one social issue came up during the debate. After some wrangling over definitions, Palin and Biden both said they opposed same-sex marriage but supported legal protections for gay couples, such as in the case of hospital visitations.

Each candidate's approach during the debate reflected their personality. Palin delivered all of her attacks with a smile and a persistently folksy style. Biden laced his scholarly responses with a bit of passion, especially when he mentioned his family.

Palin also had a third task to perform. She needed to bolster her credentials after facing increasing accusations in recent weeks that she lacked the knowledge and background in major national and international affairs to serve as the nation's No. 2. In that quest, she repeatedly touted her record as a mayor, governor, business owner and mother of five.

Biden avoided any direct attacks at Palin's background, choosing instead to direct his jabs at McCain and the Bush administration.

The closest Biden came at tweaking Palin came when he called McCain's health insurance proposal "the real bridge to nowhere," a reference to a controversial bridge in Alaska that Palin initially supported but later opposed.

Instead, Biden took exception to Palin's repeated characterization of McCain as a political maverick. "A maverick he is not," Biden asserted, citing McCain's agreements with Bush on most major issues.

Palin, meanwhile, repeatedly cited Biden's previous praise for McCain before Biden became Obama's running mate. She jabbed at Obama's judgment and accused him of advocating "a white flag of surrender" with his promise to withdraw most U.S. troops from Iraq within 16 months.

Palin also faulted Obama for failing to embrace last year's surge of troops in Iraq, strongly supported by McCain, which generally is deemed to have helped reduce the level of violence.

At the same time, Palin asserted that a McCain administration would not allow Iran to acquire nuclear weapons, and she attacked Obama's support for high-level talks with that nation and others.

Biden countered by citing calls from numerous former secretaries of state, Republicans and Democrats, for such talks. As for Iraq, Biden said Obama's views repeatedly have been embraced by the Bush administration, which recently has withdrawn some troops, and by the Iraqi government, which also has now publicly called for a U.S. withdrawal.

As for Iraq, Biden said, "John McCain has been dead wrong when it comes to the fundamentals of this war."

Afterwards, Obama campaign manager David Plouffe said Biden "showed a clear depth in foreign policy" and contended that Palin had given some incomprehensible answers.

U.S. Sen. Joe Lieberman, a Connecticut independent and a close McCain ally, praised Palin's performance and said she "proved tonight that the doubts are unfounded."

The site of Thursday's event took on added significance because Missouri is a key battleground state, and the latest polls show McCain and Obama to be in a dead heat.

Thursday's debate marked the fourth time that Washington University has hosted such a presidential event, though it was the first one to be held at the university involving the running mates.

Palin left the debate hall immediately for a rally at St. Louis University's Chaifetz Arena, where she was to be met by thousands of supporters.

The crowd there was enthusiastic during the debate, cheering so loudly at Palin's closing remarks that they drowned out half of Biden's closing.

"She did fantastic," said Mary Wilson Stake, 49, of O'Fallon, Ill. "She was very well-spoken. She had her facts put together well."

Harvey Friedman, an Obama supporter who attended the rally with family who support McCain, said he believed the debate was a draw.

"I generally thought both of them did a good job," said Friedman, 69, of Chesterfield, Mo. "Palin definitely did a better job than I thought she would."

Biden didn't join Democrats at any of several local watch parties or rallies. He flew out of town shortly after the debate to return to his home in Delaware. Biden wanted to spend time with his son, Delaware Attorney General Beau Biden, who is leaving today for Iraq as a captain with the Army National Guard.

At a Democratic gathering at the Pageant concert venue in the Loop, more than 250 gathered to cheer Biden.

David Patterson said Biden was in an untenable position.

"When he debated Hillary, no one told him not to speak condescendingly," he said. "He should be able to just debate the issues and let America see what he stands for. It's an affront that (Palin) has turned this into a freak show."

To hear aides on both sides talk before the debate, Palin planned to be combative, while Biden would appear more conciliatory.

Spokeswoman Tracey Schmitt said Palin was "going to lay out in no uncertain terms what is her record of executive leadership and Joe Biden's 35 years in the confines of Washington, D.C."

"Gov. Palin has more executive experience than Barack Obama or Joe Biden combined," Schmitt said.

Meanwhile, Obama senior strategist David Axelrod said in an interview before the debate that Biden would be emphasizing what sort of change Obama's election would bring and contrast that with McCain's.

"He didn't come here with the mind-set of tussling or a body slam," Axelrod said.

Debate viewers, he added, "are not turning in to see a sporting event. They're turning in to see a discussion of the future of this country."

Palin and Biden both flew into Lambert St. Louis International Airport in the early afternoon, just over an hour apart.

Palin sported a large bandage on her right hand. An aide said she injured it slightly when she fell while jogging this week at McCain's ranch, where she was preparing for the debate.

The moderator, Gwen Ifill, also came in with an injury; she broke her ankle earlier this week. Washington University athletic director John Schael recruited two members of the football team, starting quarterback Buck Smith and defensive lineman Tim Taylor, to help Ifill get on stage and into her chair.

Jake Wagman, Adam Jadhav, Kavita Kumar, Steve Giegerich and Todd Frankel of the Post-Dispatch staff contributed to this report.

jmannies@post-dispatch.com