RICHMOND, Va. -- Illinois Sen. Barack Obama yesterday rejected his own Democratic running mate's prediction that enemies would go out of their way to "test" him soon after he takes office, as he and his presidential rival, Arizona Sen. John McCain, wrestled with a disturbing report suggesting that terrorists are rooting for the Republican.

"Whoever is the next president is going to have to deal with a whole host of challenges internationally -- and a period of transition in a new administration is always one in which we have to be vigilant," Mr. Obama said in Richmond, flanked by national security advisers to signal his readiness to cope with whatever crises might come.

Switching gears from the economy -- his favorite campaign topic lately -- Mr. Obama addressed for the first time the assertion last weekend by his vice-presidential choice, Delaware Sen. Joseph R. Biden Jr., that adversaries will provoke an international crisis within six months "to test the mettle of this man."

Republicans have latched onto the statement, arguing that electing Mr. Obama could invite attack. In Ohio, Mr. McCain cited the statement as he stepped up criticism of his rival. "I will not be a president who needs to be tested. I have been tested; Senator Obama hasn't," Mr. McCain told supporters in Green, Ohio. "The next president won't have time to get used to office."

Mr. Obama rejected his running mate's language but embraced his larger point. "Joe sometimes engages in rhetorical flourishes, but I think that his core point is that the next administration's going to be tested regardless of who it is," the Democratic nominee said, thanks to wars in Iraq and Afghanistan, "an economy in freefall" and a host of "bad policies" by the current president, a Republican.

McCain spokesman Tucker Bounds chided Mr. Obama for trying to shrug off the concerns that Mr. Biden had voiced. "Joe Biden 'guaranteed' a generated international crisis if Barack Obama is elected, and a smile-for-the-cameras press conference isn't going to mitigate the risk of an Obama presidency," he said.

Mr. McCain spent the day defending states that President Bush won, New Hampshire and Ohio. Mr. Obama was vying for Virginia, which hasn't voted for a Democrat since Lyndon B. Johnson in 1964 -- reflecting Mr. Obama's surge in the polls.

Meanwhile yesterday, Pennsylvania's Gov. Ed Rendell said he was "nervous" about recent polling that has shown the presidential race tightening in his state and has asked Mr. Obama to return to the Keystone State to shore up support before the election. Some polls show the Democrat's lead in Pennsylvania has dipped to single digits, down from around 12 percent, the governor said before a groundbreaking ceremony for a $1.2 billion coke oven replacement project at U.S. Steel Corp.'s Clairton Coke Works.

His party's presidential nominee "came the first day after the Democratic convention and hasn't been back since," Mr. Rendell said. "[New York Sen.] Hillary [Rodham Clinton] was in on Friday, and that was a good sign. And I expect my memo asking him to return will be answered positively."

The governor also said a comment to the Post-Gazette editorial board last week by Pennsylvania Rep. John Murtha, D-Johnstown, that "there's no question Western Pennsylvania is a racist area" was "dead wrong," in Mr. Rendell's view.

"There may be some people like that here, yes. But in times like these, the vast majority of people will vote for the person who they think will help them and help them improve their quality of life," the governor said.

Mr. Obama spent an hour or so in private yesterday with national security advisers, among them former U.N. Ambassador Richard Holbrooke, former Navy Secretary Richard Danzig and Democratic former Georgia Sen. Sam Nunn, now co-chairman and chief executive of the Nuclear Threat Initiative, a charitable organization working to reduce the global threats from nuclear, biological and chemical weapons. Mr. Obama afterward said he had decided to convene the briefing two or three weeks ago to ensure that he kept up to speed on international issues.

But his focus wasn't entirely on foreign policy as he stumped in Virginia, where Democrats see a strong chance to snap their 44-year losing streak. Mr. Obama stepped up his rebuttal to allegations that his plan to roll back Bush-era tax cuts would hurt middle-class taxpayers and mark a shift toward socialism.

"It's not a very plausible argument," Mr. Obama told reporters in Richmond, reiterating that Mr. McCain had once opposed a proposal that skewed tax cuts to the wealthiest. "Was he a socialist back in 2000 when he opposed the Bush tax cuts?"