ST. LOUIS, Mo. -- Delaware Sen. Joseph R. Biden Jr. won Thursday night's vice-presidential debate, according to two national polls, giving the Democrats fresh, important momentum yesterday as the campaign for the White House enters its final month.

A CBS News/Knowledge Networks survey of 500 uncommitted voters taken after the debate Thursday night found that 46 percent thought Mr. Biden won, while 21 percent gave the victory to his Republican rival, Alaska Gov. Sarah Palin. While two-thirds found Ms. Palin knowledgeable about important issues, 98 percent said the same about Mr. Biden.

A separate CNN/Opinion Research Corp. survey found similar views, with 51 percent saying Mr. Biden did better, to 36 percent favoring Ms. Palin.

Perhaps most significant, the CNN survey found that 87 percent thought the Delaware senator was qualified to be president, while 42 percent saw Ms. Palin that way.

"He didn't ramble, and he wasn't patronizing. He stayed on message and linked McCain to President Bush in a very effective way," said political science professor Douglas Koopman of Calvin College in Grand Rapids, Mich. Particularly impressive, Dr. Koopman said, was how Mr. Biden dealt with Ms. Palin's repeated reference to her running mate, Arizona Sen. John McCain, as a "maverick."

"I love him," Mr. Biden said of Mr. McCain, his longtime Senate colleague. "He's been a maverick on some issues, but he has been no maverick on the things that matter to people's lives," such as the economy, health care and education.

Even so, reviews for Ms. Palin, whose approval numbers had been tumbling in recent weeks, were generally favorable too.

"Had Palin blown it, it probably would have been the end of McCain's candidacy, but she dug in her heels and enhanced her credibility," said associate political science professor Wayne Lesperance at New England College in Henniker, N.H.

But at this stage of the campaign, with Americans weary of war and anxious about the declining economy, the Republican ticket faces a hostile environment since it represents the incumbent party at a time when voters are seeking change.

Ms. Palin had to do more than merely hold her own to shift the campaign's overall dynamic. But there's no evidence that she did that, even if she exceeded expectations for her performance.

Mr. Biden's running mate, Illinois Sen. Barack Obama, led by an average of 5.8 points in national presidential-race surveys over the past week before the Biden-Palin debate, according to RealClearPolitics.

"Every day that goes by with Barack Obama about 5 to 8 points ahead is not a good day for John McCain," said vice-presidential expert Timothy Walch, director of the Herbert Hoover Presidential Library in West Branch, Iowa.

"Every day of the next month is important," said Obama campaign manager David Plouffe.

Nevertheless, Republicans claimed new momentum.

Ms. Palin, who has been unavailable to most of the press corps ever since she joined the GOP ticket, will "be available to the press, and she'll talk to every American voter. She'll be out 24/7," vowed McCain senior adviser Steve Schmidt.

Some experts agreed that Ms. Palin's folksy style could resonate, particularly with women in the Midwest and West -- a trend that may not show up right away. "People listen to what the neighbors say, what their favorite pundit says, and sometimes there's a disconnect between that and what the media are saying now," said Wayne Fields, a professor of English and American culture studies at Washington University in St. Louis.

Ultimately, he said, people base their opinions on their intuition, and "they really don't know specifically what they're basing their judgment on."

Yet Ms. Palin probably won't have much more opportunity to be widely heard. Public attention tends to focus most on presidential candidates, especially in the final weeks of a campaign, and there are no more vice-presidential debates.

With a crush of other big news stories -- including the House passage of the financial-rescue plan yesterday and the second McCain-Obama debate coming up Tuesday -- the Biden-Palin encounter is likely to fade quickly. "The vice presidential story is essentially over now," Dr. Walch said. "By Monday, we'll be on to another topic."

Mr. Biden yesterday was in Dover, Del., saying goodbye to his son, Beau, who is Delaware's attorney general. Beau Biden's National Guard unit headed yesterday to Texas to train for deployment to Iraq.

Ms. Palin yesterday was in Dallas for two private campaign events.