DENVER — Democrats were poised to formally deliver the party’s presidential nomination to Senator Obama today, making him the first black nominee of a major party. While the historic outcome was certain, suspense remained over how a vote of delegates would proceed, and for how long.

Speaker Pelosi, presiding officer of the Democratic National Convention, predicted roll-call voting after the names of both Mr. Obama and one-time rival Senator 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 Mrs. Clinton herself — asks the delegates to give the nomination to Mr. Obama by acclamation.

Mrs. Clinton, who made a ringing, unqualified endorsement of her former rival in a prime-time convention speech yesterday, 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.

Governor Rendell of Pennsylvania, who had been a Clinton supporter, said he expected the New York senator to say that she would cast her vote for Mr. 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,” Mr. Rendell said.

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

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

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

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

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

The letter, first obtained last night by The Associated Press, said Mrs. Clinton would have one nominating speech and two seconding speeches, followed by Mr. 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 a Obama senior adviser, Jeff Berman, a senior Clinton adviser, Craig Smith, and the convention secretary, Alice Germond.

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

Democratic officials close to Mr. 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.

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

“My horse is out of the race. I’m getting out to work for Obama,” Ms. 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, the Obama adviser, Mr. Berman, and the Clinton adviser, Mr. Smith, told delegates on today 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,” Mr. Berman said.

Anticipating tonight’s focus on national security at the convention, Senator McCain contended in a new TV ad that Mr. 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 Mr. 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.”

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