House Speaker Nancy Pelosi, presiding officer of the Democratic National Convention, predicted roll-call voting after the names of both Obama and one-time rival Hillary Rodham Clinton are put in nomination, would go "very smoothly."

"Are you ready for victory? Then you must be ready for unity. That is the only way we are going to win and have this victory," she told Iowa's convention delegates.

Many details remained unknown, however, including how many states would vote before somebody - probably Clinton herself - asks the delegates to give the nomination to Obama by acclamation.

Clinton, who made a ringing, unqualified endorsement of her former rival in a prime-time convention speech Tuesday, planned to meet with all her delegates in early afternoon and was expected to make a statement at that time. She won 18 million votes in primary-season contests but failed to earn her party's nomination.

Pennsylvania Gov. Ed Rendell, who had been a Clinton supporter, said he expected the New York senator to say that she would cast her vote for Obama.

"I'm going to cast my vote for Senator Obama if Hillary Clinton says she's going to cast her vote for Senator Obama," Rendell said.

Obama, who was due to arrive in the convention city mid-afternoon Wednesday, will give his acceptance speech on Thursday to as many as 75,000 people at nearby Invesco Field at Mile High Stadium.

Then, on Friday, Obama, his wife Michelle and running mate Joe Biden and his wife Jill will embark on a bus tour of battleground states Pennsylvania, Ohio and Michigan.

Biden was to address the convention Wednesday night, as was former President Clinton, whose support for Obama has seemed tepid at best. Earlier this month, for instance, the former president sidestepped a question on whether Obama was prepared for the White House. "You could argue that no one's every ready to be president," Clinton told ABC News.

Representatives of the Clinton and Obama teams struck a deal setting ground rules for Wednesday's roll call vote that will hand the nomination to Obama, but will also allow Clinton supporters to express their support for her.

Advisers to Clinton and Obama sent a joint letter to state delegation chairs instructing them to distribute vote tally sheets to delegates Wednesday and return them before the vote gets under way.

The letter, first obtained Tuesday night by The Associated Press, said Clinton would have one nominating speech and two seconding speeches, followed by Obama's nominating speech and three seconding speeches - totaling no more than 15 minutes for each candidate. Then the roll call will begin, said the letter signed by Obama senior adviser Jeff Berman, Clinton senior adviser Craig Smith and convention secretary Alice Germond.

The roll call will continue until all votes are counted or someone asks the delegates to give the nomination to Obama by acclamation.

Democratic officials close to Clinton say they plan to have someone - perhaps the senator herself - cut off the vote after a few states.

Yet to be announced: who would make the nominating speeches and how long the roll call vote would be allowed to proceed.

Kathleen Krehbiel, an Iowa delegate who had supported Clinton, credited the New York senator's convention speech for finally persuading her to cross the line and vote for Obama.

"My horse is out of the race. I'm getting out to work for Obama," Krehbiel said. But, she added, "I think there are a few delegates who need to vote for Hillary to reach that point of closure."

In a sign of unity, Obama adviser Berman and Clinton adviser Smith told delegates on Wednesday that they have been working out of the same office all week to ensure a smooth convention.

"The story is that we are working as a team," Berman said.

Anticipating Wednesday night's focus on national security at the convention, Republican John McCain contended in a new TV ad that Obama showed he was "dangerously unprepared" for the White House when he described Iran as a "tiny" nation that didn't pose a serious threat.

"Iran. Radical Islamic government. Known sponsors of terrorism. Developing nuclear capabilities to 'generate power' but threatening to eliminate Israel," says the ad, which was being run in key states. "Terrorism, destroying Israel - those aren't 'serious threats"'?

Missing from the ad was the context of Obama's remarks last May in which he compared Iran and other adversarial governments to the superpower Soviet Union. "They don't pose a serious threat to us the way the Soviet Union posed a threat to us," he said in arguing for talks with Iran. "You know, Iran, they spend one-100th of what we spend on the military. If Iran ever tried to pose a serious threat to us, they wouldn't stand a chance."

Bill Clinton in his speech was expected to criticize McCain and on the Bush administration, particularly on the state of the U.S. economy.