DENVER – Democratic delegates began marking their presidential nominating ballots Wednesday, making the unprecedented choice between a black man and a white woman. But only a limited number of the ballots were expected to be counted in an afternoon roll call before Barack Obama was declared the party's presidential nominee by acclamation.

With the convention balloting just hours away, delegates still were waiting to hear which states would participate in the roll call before it was cut off in unanimous support for Obama. The abbreviated vote was the result of a deal between Obama and Hillary Rodham Clinton so that some of her backers could express their support without dragging out a divided process.

The deal was short on specifics, though. Delegates still were not clear which states would get to participate in the roll call. State delegation chairs were simply instructed in a joint letter from Clinton and Obama advisers to distribute ballots to delegates Wednesday morning and return them no later than 4 p.m., when voting is scheduled to get under way.

Sonja Jaquez Lewis, a Clinton delegate from Boulder County in Colorado, said she and others may walk out if Clinton is denied a roll call.

“If we don't have an official roll call vote state-by-state, it is going to reopen a wound,” said Lewis, adding that she would do whatever Clinton asks of her delegates.

Clinton planned to meet with her delegates a few hours before an afternoon session where both she and Obama would be nominated. She has said she will vote for Obama, but not tell her delegates how to vote.

Kathleen Krehbiel, Clinton's Iowa vote-counter, said Clinton loyalists had not received any specific guidance, but she believed most would cast their ballots for Obama. She said she made up her mind to do so after Clinton encouraged support for Obama in a speech Tuesday night.

“I did not want to see a floor fight,” Krehbiel said as Iowa delegates received their ballots. “I don't see any further reason to continue to carry out a pretense that she's a candidate. She's not.”

But, Krehbiel said, “I think there are a few delegates who need to vote for Hillary to reach that point of closure.”