NEW YORK — For an audition to be second fiddle, tomorrow's debate between often ill-informed newcomer Sarah Palin and often gaffe-prone veteran Joe Biden offers unusually large pitfalls — and promise.

For once, the whole world may be watching. Already, 3,100 media credentials have been issued, the most the Commission on Presidential Debates ever needed in seven vice presidential debates it's hosted.

The attention is driven by the public's fascination with Palin, the first-term Alaska governor that Republican presidential candidate John McCain plucked from relative political obscurity to be his running mate.

Initially, Palin was praised as a superb political communicator for the delivery of her acceptance speech at the Republican National Convention four weeks ago. She energized the party's conservative base, which had reservations about McCain, and quickly showed she could outdraw McCain on the stump — a likely factor in their decision to appear together more often than running mates usually do.

But a series of shaky Palin television interviews has left even some conservatives questioning whether she is ready to be vice president. She couldn't describe the Bush doctrine in foreign affairs, seemed to have little grasp of the proposed financial industry bailout and even appeared to endorse Democratic presidential candidate Barack Obama's position on chasing al-Qaida terrorists in Pakistan.

Palin's performance against Biden, the Delaware Democrat with 35 years in the Senate, could restore her initial luster or seriously weaken the GOP ticket.

Last week's Obama-McCain debate appeared to give the Illinois Democrat a small boost in the polls but produced no knock-out blows. So the vice-presidential debate at Washington University in St. Louis could be a pivotal moment in a race already filled with surprising twists.

Palin herself outlined the contest in an interview that aired yesterday on the "CBS Evening News With Katie Couric."

"He's got a tremendous amount of experience, and you know, I'm the new energy, the new face, the new ideas, and he's got the experience based on many, many years in the Senate, and voters are gonna have a choice there of what it is that they want in these next four years," Palin told Couric.

Palin left the campaign trail Monday to prepare at McCain's ranch in Sedona, Ariz. She is being coached by McCain's top campaign strategist, Steve Schmidt, as well as advisers Tucker Eskew, Nicolle Wallace and Mark Wallace, all veterans of President George W. Bush's political operation.

McCain strategists are well aware Palin's glowing image has been badly bruised since the convention.

She's been kept from nearly all contact with reporters except for a handful of high-profile network TV interviews that revealed her relatively thin grasp of foreign policy and domestic issues. Palin's answers have become punch lines for comedians, and a mocking Palin impersonation by Tina Fey on "Saturday Night Live" has become a television and YouTube sensation.

So Palin is under heavy pressure to show a passing command of issues facing the next president.

"I don't think she can get away with comments on foreign policy like she knows about Russia because it's near Alaska," Minnesota-based Republican strategist Tom Homer said. Palin needs to "show ability to think on her feet and to engage with someone on the level of Sen. Biden without a TelePrompTer in front of her," Homer added.

Biden, for his part, was prepping at home in Wilmington, Del. On hand to help were top Obama campaign strategists David Axelrod, Anita Dunn and Ron Klain, who helped coach Vice President Al Gore four years ago.

A veteran debater after his Senate experience and his own two short-lived presidential campaigns, Biden has his own set of challenges.

His first presidential bid in 1987 ended after he appropriated the life story of British politician Neil Kinnock during a Democratic primary debate in Iowa. Even now, his off-the-cuff speaking style still produces verbal blunders, like when he mused aloud recently that Hillary Rodham Clinton might have made a better running mate for Obama.

And his reputation as a windy orator will be tested by the tight debate format, which allows 90-second answers and 2-minute follow-ups.

In addition, Biden will be debating a female candidate who has excited many women and elicited sympathy over some attacks perceived as sexist.

"Biden's advisers have to keep beating into his head that his normal style ... can be offensive," GOP strategist Ed Rollins said. "He has a tendency, like a lot of senators, to talk down to people. And that's a danger for him because there are an awful lot of women out there who relate to Palin."