Democratic Sen. Barack Obama moved quickly yesterday to capitalize on Republican Sen. John McCain's inability to say how many residences his family owns.

Politico, a political news Web site, asked McCain "how many houses do you and Mrs. McCain have," and the site published his answer ("I think — I'll have my staff get to you") yesterday morning.

By mid-day the Obama campaign had made a TV ad, slated events in 16 states, circulated audio of the response and posted a YouTube video of Obama calling the remark proof of McCain's "gap of understanding" between his world and the real world.

Also yesterday, Obama said he's decided on a running mate, but he won't say who it is.

"I've made the selection, that's all you're gonna get," he said in Virginia.

Obama plans to announce his choice in a text message to supporters sometime before tomorrow afternoon, when he's scheduled to appear in Illinois with his running mate, just two days before the Democratic National Convention kicks off in Denver.

Asked by a reporter when the text would be sent, Obama grinned and said, "Wouldn't you like to know?"

Of his options, the Illinois senator said, "We had some great choices." He indicated he was not picking someone who would march in lock-step with him.

"I want somebody who's independent, somebody who can push against my preconceived notions and challenge me so we have got a robust debate in the White House," he said.

McCain has also been coy about releasing information about his vice presidential selection, although word surfaced in recent days that he was considering a candidate who favors abortion rights or even a former member of a Democratic ticket — Connecticut Sen. Joe Lieberman, Al Gore's vice presidential nominee in 2000 who since was re-elected to the Senate as an independent.

The Arizona senator made no comment about his selection yesterday.

His announcement was widely expected to be made the Friday after next week's Democratic convention, which is also McCain's 72nd birthday. That timing could serve to lessen Obama's momentum while escalating GOP enthusiasm leading to its gathering, which begins three days later.

OBAMA ON ATTACK

In Chester, Va., Obama took issue with McCain adviser Phil Gramm's view that the United States is in a "mental recession," McCain's jokey definition last weekend of rich (a $5 million income) and McCain's comment Wednesday that the economy is fundamentally strong.

"If you don't know how many houses you have, then it's not surprising that you might think the economy was fundamentally strong. But 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.

McCain's campaign says the Arizona senator has four residences: condos in Phoenix, Arlington, Va., and Coronado, Calif., and a house in Sedona, Ariz. All are owned by his wife, Cindy, and their children, who also own eight other residential properties.

Those include four other houses at the 15-acre Sedona spread and four more condos, according to real estate records and the senator's financial disclosure reports.

The dozen properties are worth more than $10 million, current assessments show.

McCain spokesman Brian Rogers said yesterday that Obama is out of touch.

"Does a guy who made more than $4 million last year, just got back from vacation on a private beach in Hawai'i and bought his own million-dollar mansion with the help of a convicted felon really want to get into a debate about houses?" asked Rogers.

Hawai'i has no private beaches. Obama, who was born in Honolulu and spent most of his youth there, visited relatives during a recent vacation and joined the public swimming and surfing in the ocean.

MCCAIN RESPONDS

By yesterday evening, the McCain team had released an ad about Obama and his former fundraiser Antoin Rezko, who was convicted of corruption charges in June. On the same day in 2005, Obama bought his house and Rezko's wife bought an adjoining lot owned by the same sellers. She later sold a strip of it to Obama.

McCain, who has portrayed Obama as the elitist in the race, is the son and grandson of admirals. The Associated Press estimates his wife, a beer heiress, is worth $100 million.

Obama was raised by a single mother who relied at times on food stamps, and went to top schools on scholarships and loans. His income has increased from sales of books he wrote since he spoke at the 2004 Democratic convention.

The Associated Press and the Los Angeles Times contributed to this report.