Gov. Sarah Palin and Sen. Joseph R. Biden Jr. sparred last night in perhaps the most anticipated, though not necessarily the most memorable, vice presidential debate in political history.

Through a civil but feisty 90 minutes, the rivals pressed home familiar arguments on health care, the Iraq War, the economic crisis and other issues. What the session lacked was any obvious game-changing gaffes or mistakes for either candidate.

And that, given the burden of expectations surrounding the evening, was a plus for Ms. Palin. Her first debate on the national stage followed recent television network interviews in which she made missteps that, fairly or unfairly, drove down expectations for her performance last night.

But both Ms. Palin and Mr. Biden turned in generally strong performances. Neither was ever knocked off stride in the questioning from moderator Gwen Ifill of PBS.

Despite occasional sharp differences, the tone of the session at Washington University in St. Louis was almost uniformly friendly, in contrast to the frostier atmosphere at last Friday's encounter between the presidential contenders, Republican John McCain and Democrat Barack Obama.

"Nice to meet you. Can I call you Joe?" Ms. Palin asked as the two smiling contenders greeted one another on stage.

Ms. Palin's demeanor seemed often deliberately folksy, offering her "Wasilla Main Street" views as an antidote to Washington insiderism while showing a general command of the issues.

Mr. Biden, naturally enough, projected a more senatorial persona, and was often more direct in his answers. He too offered his own homespun credentials, describing his encounters with constituents at Home Depots and local restaurants.

Responding to his first question, Mr. Biden defended the financial rescue plan that he and the two presidential nominees had just approved, but he quickly used it to shift to an assault on the economic policies of the Bush administration, which he then tied to Mr. McCain.

Ms. Palin opened her discussion of the economy with the suggestion that a Saturday morning soccer game would provide a good barometer of the nation's fiscal health

"I betcha you're going to hear some fear in that parent's voice," she said in anticipating the average person's reactions to the problems of the economy.

She portrayed her running mate as an early voice against abuses on Wall Street.

"He sounded that warning bell; his colleagues didn't want to listen to him,'' she said.

Mr. Biden maintained that it was his partner that was prescient on the dangers of subprime mortgage lending. Mr. McCain, he said, was a champion of the deregulation and self-regulation that brought on the crisis in confidence in the financial sector.

Both candidates aimed most of their volleys not at the opponent on stage but at the figure atop the opposing ticket. Mr. Biden wasted no time in reminding viewers of Mr. McCain's statement two weeks ago that the economy was fundamentally sound.

"He was talking to and he was talking about the American work force ... the greatest in this world," Ms. Palin said in rebuttal. With a wink, she added, "That's what John McCain meant."

On foreign policy, Ms. Palin repeated her partner's frequent criticism of Mr. Obama for failing to support the military's "surge" policy in Iraq.

Mr. Biden had a familiar rebuttal in tying Mr. McCain to the administration's record in Iraq and arguing that the Republicans had jeopardized the nation's larger strategic interests by focusing on Iraq to the exclusion of more crucial security threats in Pakistan and Afghanistan.

Ms. Palin insisted that the Democratic plan for a timetable for U.S. withdrawal from Iraq amounted to "waving the white flag of surrender," Mr. Biden countered that even the Bush administration was now negotiating a timetable for withdrawal with the Iraqi government, leaving Mr. McCain as a lonely voice in opposition to such a plan.

"John McCain has been dead wrong on the fundamental issues related to the conduct of the war," he said. "Barack Obama has been right. Those are the facts."

On health care, Ms. Palin touted the Republican plan to offer a $5,000 tax credit to allow for the purchase of individual insurance polices. Mr. Biden criticized the plan for a parallel feature that would end tax preference for employer paid health insurance, meaning, he said, that it would effectively impose a tax increase on most recipients.

The evening's most emotional moment came near the end when Mr. Biden, recalling his sons' recuperation from the auto accident that killed his first wife, came close to choking up.

Both candidates struck gracious notes in acknowledged and saluting the military service of their sons. One of Ms. Palin's sons was inducted into the Army shortly after she emerged as the GOP vice presidential choice. Mr. Biden will attend a ceremony today at which his son's National Guard unit prepares for service in Iraq.

The stakes were high for both candidates, but the focus was unmistakably on Ms. Palin. The first-term governor had electrified the Republican base when she emerged as Mr. McCain's surprise choice the weekend before the Republican National Convention. More recently, however, her stock had fallen with a series of halting performances in some of the relatively few interviews that the McCain camp has permitted her to do.

Surveys released this week suggested that the candidate that had given the GOP ticket a shot of adrenaline in early September was now turning into a potential liability in the minds of some voters, particularly crucial independents.

Debate-eve polls from both the Washington Post and the Pew Foundation showed a drop in her favorability ratings. The Post survey found that six in 10 voters believe Ms. Palin was not qualified to be president. The Pew Research survey also suggested that a majority of voters believe she does not have enough experience to be president.

But if Ms. Palin had stumbled on some earlier television appearances, she turned in strong, and, on the evidence, winning performances in a series of debates that led to her election as Alaska governor two years ago. One rival said then that it was a mistake to view their encounters in terms of classic debate scoring. She did well in those encounters in large part because she simply projected a likable persona that voters felt comfortable with.

The vice presidential encounter was the subject of intense anticipation, but it could be quickly forgotten depending on the outcome of the pending House vote on a rescue package for the nation's credit system. The Senate vote on the measure the previous day was a reminder of how much the nation's economic woes have begun to dominate a campaign in which the Iraq War and health care once vied as the voters' chief concern.

In part because of the recent preoccupation with the economy, an issue on which polls have shown more voters trust Mr. Obama, the Democratic ticket has gained momentum over the last ten days. Before last night, the Democrats had moved to a small but consistent lead in national polls.

That fact placed one more level of stress on Ms. Palin last night as the Republican are under pressure shift the inertia of a race whose recent movement has been in a Democratic direction.

There are still four weeks to go before Election Day.

For weeks ago this race looked very different, so there is still time for its dynamics to change again.