Democrat Barack Obama described his vice presidential pick as independent, ready to be president if needed, and strong on the economy, but he still has not identified his choice.
Meanwhile, the Democrat heaped new criticism on his Republican rival John McCain in a push to blunt attacks that have narrowed his lead in the polls. Obama on Thursday chided McCain for an interview in which he said he did not know how many homes he owns, and he branded the Republican as rich, out-of-touch with voters and touting inflated foreign policy credentials.
Obama planned to disclose his running mate choice by unleashing text messages to supporters, perhaps as early as Friday. He is scheduled to appear with his No. 2 Saturday at a massive rally in his home state of Illinois and undertake a tour of battleground states before the Democratic National Convention starts Monday in Denver.
"I've made the selection, that's all you're gonna get," Obama told reporters while campaigning in Virginia on Thursday.
While Obama has remained tight-lipped about his selection, the field of candidates appears to have been narrowed down to four: Govs. Kathleen Sebelius of Kansas and Tim Kaine of Virginia, Sen. Evan Bayh of Indiana, and Sen. Joe Biden _ the Senate's top Democratic foreign policy expert. An announcement is expected to be made in a text message to supporters sometime before the Saturday event.
In a TV interview with CBS aired Friday morning, Obama outlined his criteria for his running mate: "Obviously, the most important question is: Is this person ready to be president?"
Second, he said, was: "Can this person help me govern? Are they going to be an effective partner in creating the kind of economic opportunity here at home and guiding us through some dangerous waters internationally?"
And, he added: "I want somebody who is going to be able to challenge my thinking and not simply be a 'yes person' when it comes to policymaking.
On the Republican side, party officials said late Thursday that McCain has not settled on a running mate, although former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty were under serious consideration. Two officials close to Romney said he had not been offered the job.
The Arizona Republican is expected to announce his choice between next week's Democratic convention and his own Republican convention in St. Paul, Minnesota, that begins Sept. 1. It's possible he could do it on Friday, Aug. 29, the day he turns 72 and the day after Obama accepts his own nomination in Denver. But no plans are set and McCain might wait until his own convention week.
Officials said the campaign also was preparing for an "unconventional" nominee, an indication that oft-mentioned former Pennsylvania Gov. Tom Ridge, an abortion-rights supporter, or Connecticut Democrat-turned-independent Joe Lieberman still could be in the running. That category also could include non-politicians who McCain deeply admires, such as Gen. David Petraeus, the top U.S. commander in Iraq.
The need for a careful selection for the vice presidency for both candidates comes as McCain has largely erased Obama's lead in the polls.
To counter the perception that his campaign has stalled, Obama has stepped up his attacks even as some supporters worry that someone who campaigned on themes of hope and change can be aggressive enough.
After being introduced Thursday at a rally in Richmond, Virginia, by Kaine, Obama criticized McCain for not being able to answer a question about how many homes he owns during an interview. McCain's wife, Cindy, is an heiress to a large beer distributorship and her wealth is estimated to be at least $100 million.
"If you're like me, and you've 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, you might have a different perspective," Obama said.
Obama also struck a defensive tone, saying that despite his limited experience on the national stage, he has shown better judgment on foreign affairs than McCain has.
"I will put my judgment on foreign policy over the last five years against John McCain's anytime. Anytime," Obama said.
McCain has derided Obama's call for a withdrawal timetable as political opportunism aimed at getting himself elected at the cost of losing the war.
Associated Press writer Liz Sidoti contributed to this report from Washington.