Obama was on a two-day bus tour through Virginia, a likely battleground state, amid frenzied speculation about when he would announce his running mate. He brushed off questions about his choice during a morning visit to a farmers' market in Greensboro, N.C., before boarding the bus.

Obama was to spend the night in Richmond and campaign today with Gov. Tim Kaine, widely believed to be on the short list of possible running mates.

Former Gov. Mark Warner, who campaigned with Obama yesterday and will deliver the keynote speech at next week's Democratic National Convention in Denver, told reporters that Kaine would be a "great choice" but that he had no clue whether he would be picked.

At a community college in Martinsville, Obama told about 350 supporters that McCain had a compelling biography as a former prisoner of war in Vietnam. But, he said, the GOP candidate would follow the economic policies of the Bush administration if elected. "I honor his service," Obama said. "I don't honor his policies. I don't honor his politics."

On Tuesday, Obama had asserted that his rival was questioning his "character and patriotism" in his stance on the Iraq war and challenged McCain to stop.

McCain, in a town-hall meeting in Las Cruces, N.M., said Obama "got a little testy on this issue."

"Let me be clear - I am not questioning his patriotism," McCain said. "I am questioning his judgment."

McCain then pressed his attack. "Washington is full of talented talkers," he said. "The bottom line is that Sen. Obama's words, for all their eloquence and passion, don't mean all that much."

As the campaign turns increasingly negative, and as new national polls show McCain starting to erode an edge Obama has held all summer, both men unveiled fresh attack ads.

Again trying to tie McCain to the unpopular President Bush, Obama's TV commercial asks: "Can we really afford more of the same?" It slams McCain's tax plan as a giveaway for big corporations and oil companies.

McCain's radio ad says: "Celebrities like to spend their millions. Barack Obama is no different. Only it's your money he wants to spend."

Financial documents filed yesterday with the Federal Election Commission showed that McCain spent $32 million in July, with nearly $2 of every $3 devoted to advertising.

McCain reported raising more than $26 million during the month. He began August with more than $21 million in the bank. His aggressive media strategy - he spent nearly $19 million on advertising spots - kept him on the air as much as Obama.

The deadline for filing July financial reports was 12:01 a.m. today. Obama had not yet submitted his, but the campaign announced last weekend that he had raised more than $51 million in July.

In Martinsville, Obama stuck mostly to economic themes, adopting a pitch that sounded much like Hillary Rodham Clinton in the waning days of her primary campaign.

"If you give me that opportunity, if you give me that chance, I will fight for you every single day," he pledged. "I'll wake up every day in that White House thinking about those people in Martinsville."