RICHMOND -- Democratic presidential candidate Barack Obama wrapped up a two-day campaign swing through Virginia on Thursday by sharpening his criticism of Republican rival John McCain and keeping people guessing about his choice of a running mate.

Obama appeared with Gov. Tim Kaine at an event in Chesterfield County, heightening speculation about Kaine's prospects for joining Obama on the ticket.

Obama is expected to announce his decision by Saturday, when he is scheduled to appear with his running mate in Illinois. Kaine and his senior staff met privately with Obama for about 15 minutes at a Richmond hotel Thursday morning, but the governor would not say whether he has been told of Obama's decision.

"I'm going to let the campaign take it from here," Kaine told reporters after speaking at a drunken-driving prevention event in Hanover County on Thursday afternoon. "They're going to reveal what they want to reveal when they want to reveal it," said Kaine, a national co-chairman of Obama's campaign. "Again, it's been nice to be mentioned, but I'm going to let them do the heavy lifting from this point."

Kaine said he plans to fly to Denver tonight in advance of the Democratic National Convention, which begins Monday. The governor has yet to appear on the convention's speaking schedule, but said Thursday that "we have in been discussions with them and they will announce the schedule when it is set."

Kaine said he hopes to make a "family vacation" out of convention week.

"We'll see how much downtime we're getting," he said.

Kaine introduced Obama at an outdoor, town hall-style meeting at John Tyler Community College in Chester, where more than 200 supporters gathered in a tree-shaded picnic area to hear the Democrats.

Kaine was the first governor outside of Obama's home state to endorse the Illinois senator, and called his involvement with Obama's campaign "one of the most amazing and exciting experiences of my life."

Obama used the event as a forum to draw contrasts with McCain on economic issues, portraying McCain as out of touch with the concerns of working families.

Obama sounded similar themes during Wednesday visits to Martinsville and Lynchburg, but he was armed with fresh material Thursday.

Obama seized on a story published by news organization The Politico in which McCain revealed he was unsure how many homes he owns. After telling the audience that McCain owns seven homes, Obama said the Republican is disconnected from the anxieties of people struggling to make mortgage payments and cover rising food and energy costs.

"If you don't know how many houses you have, then it's not surprising that you might think the economy is fundamentally strong," Obama said. "But if you're like me, and you got one house, or you are like the millions of people who are struggling right now to keep up with their mortgage so they don't lose their home, then you might have a different perspective."

McCain's campaign was quick to hit back, depicting Obama as an elitist and reminding reporters that the Democrat purchased his Chicago home with the help of a political contributor who was later convicted on unrelated fraud and bribery charges.

"Does a guy who made more than $4 million last year, just got back from vacation on a private beach in Hawaii and bought his own million-dollar mansion with the help of a convicted felon really want to get into a debate about houses?" said McCain spokesman Brian Rogers in a written statement. "Does a guy who worries about the price of arugula and thinks regular people 'cling' to guns and religion in the face of economic hardship really want to have a debate about who's in touch with regular Americans?"

Obama also responded to McCain's charges that he would increase taxes and pursue policies that would create "economic disaster." Obama said he would eliminate tax breaks for the wealthy initiated by President Bush, but provide tax relief for middle class families.

"First of all, the economic disaster is already here," Obama said, drawing applause. "But the second thing is, under my plan, 95 percent of families will get a $1,000 tax break."

In a question and answer session with the audience, Obama responded to criticism that he lacks sufficient experience in foreign affairs and national security.

Obama, a persistent critic of the war in Iraq, argued that he has shown better judgment than McCain, a strong supporter of the war.

"I will seek the best advice possible on these issues, but just take a look the track record over the last five years and I am happy to have that debate with John McCain about who has better foreign policy credentials or better judgment," Obama said.