NEW YORK - For an audition to be second fiddle, Thursday'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 have 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 set to air Tuesday night 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.