Condoleezza Rice (search) isn't the only one with a lot riding on her appearance Thursday before the Sept. 11 commission.

If panel members appear politically motivated in their questioning of the national security adviser, it could raise questions about their credibility — and the findings in their final report this summer.

Thomas H. Kean (search), the panel's Republican chairman, says he and Democratic vice chairman Lee Hamilton (search) are mindful of the political overtones in a presidential election year.

They issued an edict to fellow commissioners after last week's politically charged testimony from former government counterterror chief Richard Clarke (search). The message: Leave politics out of it.

"In a very difficult atmosphere, in a town that is the most polarized I've ever seen, the commission is trying to do a job for the American people that is to the best of our ability nonpolitical," Kean said in an interview. "That is enormously hard to do, but I think we can get it done and people should leave us alone."

Nolan McCarty, a Princeton University professor of politics and public affairs, said Rice's testimony will offer a stern test for the panel.

"Partisanship is almost inevitable," he said. "There's going to be pressure from all quarters to reach specific conclusions either in exonerating the current administration or blasting the previous administration or the reverse. This may be the low point."

Kean, a former New Jersey governor, expressed frustration with people in Washington who he said are intent on politicizing the commission's work. While panel members are political appointees who have diverse points of view and different constituencies, they are fair-minded and get along well, he said.

The 10-member panel, made up of five Republicans and five Democrats, was criticized by some relatives of Sept. 11 victims after two GOP commissioners sharply questioned the motivations of Clarke, who testified that President Bush hadn't considered the al-Qaida threat an urgent priority.

The commissioners, Fred Fielding, who served as President Reagan's legal counsel, and former Illinois Gov. Jim Thompson, received calls from the White House during Clarke's testimony. Kean said that in those calls the two were acting as go-betweens in hopes of getting Rice to testify that day.

But some relatives wondered whether the White House fed them information for their questioning of Clarke. They worry that more partisanship might be in store during the Rice hearing.

"I think the fix is in," said Debra Burlingame, whose brother had been the pilot of American Flight 77, which crashed into the Pentagon. "There will be partisan elements of that panel who will be looking for a way to embarrass or discredit the Bush administration," she said.

This isn't the first time the commission has had to fend off questions about the political leanings of members. Other questions involve:

— Commission executive director Philip Zelikow's ties to the Bush administration. Zelikow served on the Bush transition team for taking office and is friends with Rice, who co-wrote with him a 1995 book on German history. Zelikow has recused himself from the panel's proceedings dealing with Rice and the Bush transition.

— Commissioner Jamie Gorelick's ties to the Clinton administration. Gorelick served as deputy attorney general under Janet Reno. She, like Zelikow, has answered questions from commission staff about periods when she served. She has recused herself from those parts of the probe.

— Commissioner Bob Kerrey's motives. The former Democratic senator from Nebraska's impassioned questioning about pre-Sept. 11 military options to Bush and Clinton Cabinet members during the last hearing prompted some to speculate he was positioning himself to be a vice presidential choice for Democrat John Kerry. Kerrey has laughed off the suggestion.

Larry Sabato, director of the University of Virginia Center for Politics, said the panel has an enormously difficult task when it issues its report in July. A politically divided report would undermine public confidence in its objectivity, while the findings in a unanimous one could be watered-down, he said.

"The stakes are so high in a presidential year," he said. "The commission's goal from the beginning is to have a unanimous report. If that is true, it nearly guarantees that it blames both the Clinton and Bush administrations. The report essentially writes itself, and they haven't uncovered anything earth-shattering."

If the commission succeeds in looking nonpartisan during Rice's 2 1/2 hours of testimony, they will have little time to bask in the accomplishment. Next week there's a two-day public hearing that will include testimony from Reno, CIA Director George Tenet, FBI  Director Robert Mueller, former FBI Director Louis Freeh and Attorney General John Ashcroft.