"I will have something to say about that fairly soon," Obama told Bob Schieffer. "Obviously, there's been a lot of talk. It's something that I've been considering. I've said I've been considering it. And we'll be making an announcement fairly soon."
When pressed for a more specific timetable, Obama only smiled and said, "It will be pretty soon."
Obama and Senator Hillary Rodham Clinton have both hired senior aides while courting potential supporters in Iowa, New Hampshire and other key states.
Iowa's caucuses will kick off the nominating campaign in January 2008, to be followed by caucuses in Nevada and primaries in New Hampshire and South Carolina.
Clinton, who is on a weekend trip to Iraq, also has hired staff, met with activists and tried to settle on a Washington-area location for her campaign headquarters.
The moves by the two come as Democratic Senator Chris Dodd launched his campaign this week and New Mexico Governor Bill Richardson prepared to make an announcement before the end of the month.
Obama and Clinton would clearly be the Democratic field's heavyweights — one vying to be the nation's first black president, the other the country's first female chief executive.