DENVER (By John M. Broder, NYTimes) August 27, 2008 – Senator Barack Obama, the Hawaiian-born son of a father from Kenya and a mother from Kansas, officially became the presidential nominee of the Democratic Party on Wednesday, capping a meteoric rise from a little-known state senator to the first African-American to win a major-party nomination.

Although there was some suspense over how the nomination process would play out, in the end, Senator Hillary Rodham Clinton released her delegates before the roll call to vote for Mr. Obama and announced that she was voting for Mr. Obama and his running mate, Senator Joseph R. Biden Jr. of Delaware.

At the urging of Mrs. Clinton, the New York delegation cast its votes for Mr. Obama, and at 4:48 p.m. local time, Mrs. Clinton called on the Democratic National Convention to end the roll call and nominate him by acclamation.

“With eyes firmly fixed on the future in the spirit of unity, with the goal of victory, with faith in our party and country, let’s declare together in one voice, right here and right now, that Barack Obama is our candidate and he will be our president,” Mrs. Clinton said.

“I move that Senator Barack Obama of Illinois be selected by this convention by acclamation as the Democratic nominee for president of the United States.”

The crowd in the Pepsi Center roared as one and then began to chant, “Hillary, Hillary, Hillary.”

The moment concluded one the quickest rises in American political history. In just four years, Mr. Obama rose from obscurity as an Illinois state senator to the Democratic presidential nomination in a year that favors the party against the Republicans. His trajectory was launched at the last Democratic national convention, in Boston, when he electrified the delegates with a speech about his multi-ethnic roots and his vision for a colorblind America.

The roll call proceeded according alphabetically from Alabama, with Mr. Obama racking up a large but not decisive margin. California, with 441 delegate votes, and Illinois, with 185, passed when their turns came to cast their votes. When New Mexico’s turn came, Mr. Obama had a lead of more than 1,000 delegates but was still more than 500 votes short of the 2,210 needed to secure the nomination.

New Mexico ceded its position in the roll call to New York, whose delegation, led by Mrs. Clinton, entered the hall well after the count began.

She then called on the convention to declare Mr. Obama the nominee by acclamation. The band struck up the song, "Love Train," the 1960’s hit by the O’Jays, and delegates danced in the aisles.

Mr. Obama was formally nominated by Michael Wilson of Florida, a Republican and Air Force medic and veteran of Iraq.

“I’ve seen war up close - not as a political slogan or some think-tank theory,” Mr. Wilson said. “I support Barack Obama because America needs a president who has the strength, wisdom and courage to talk to our enemies and consult with our allies. A president who has the judgment to use war as a last resort, not a first resort. A president who can adapt to new situations as things change, instead of being stuck in the past.”

As a symbolic gesture of respect to Mrs. Clinton for her strong showing in the primaries and her historic role as a woman candidate, her name was put in nomination by three of the 1,640 delegates who came to the convention pledged to support her: Dolores Huerta of California, Jordan Apollo Pazell of Utah and Denise Willams Harris of New York. Ms. Huerta is co-founder of the United Farm Workers Union.

With that bit of historic housekeeping behind them, the delegates turned to eager anticipation of speeches tonight by former President Clinton and Mr. Biden.

Mr. Obama himself arrived in Denver Wednesday afternoon. He recently gave reporters a brief hint of the acceptance speech he will deliver at Invesco Field at Mile High Thursday night. “I’m not aiming for a lot of high rhetoric,” Mr. Obama said. “I am much more concerned with communicating how I intend to help middle-class families live their lives.”

The formal nomination of Mr. Obama will not completely end the drama that has riven the Obama and Clinton camps and provided a consuming story line of this convention. At 7 p.m. local time, former President Bill Clinton is scheduled to address the convention, whose theme for Wednesday is foreign policy and a tribute to the military.

A draft of Mr. Clinton’s speech will be sent to the Obama campaign Wednesday afternoon, a Clinton aide said. Mr. Obama has said in recent days that the former president free to talk about whatever subject he chooses, though he has been granted only 10 minutes of podium time (though that might change). Mr. Clinton’s aides said he intends to deliver an impassioned plea for Democratic unity and an end to what he will characterize as the fiscal and foreign policy disasters of the Bush administration.

An aide to the former president said Mr. Clinton would be as supportive of Mr. Obama as Mrs. Clinton was in her 23-minute address on Tuesday.

"It’s as strong as she was in every respect," the aide said. "And shorter."

Mrs. Clinton silenced some fears among Obama supporters that her endorsement of her bitter primary rival would be less than total with a well-received speech on Tuesday night.

With her husband watching from a skybox, Mrs. Clinton rallied her supporters behind Mr. Obama, saying there was no more important task facing them and the country, regardless of any lingering ill will.

“Whether you voted for me, or voted for Barack, the time is now to unite as a single party with a single purpose,” Mrs. Clinton said Tuesday night to loud applause. “And you haven’t worked so hard over the last 18 months, or endured the last eight years, to suffer through more failed leadership.”

Mr. Clinton’s speech on Wednesday will be followed by the nomination of Senator Joseph R. Biden Jr. of Delaware as the party’s vice-presidential candidate and finally by Mr. Biden’s acceptance speech.

Mr. Biden’s task, in what will be the most important speech in his 36-year career in politics, will be to wrest the convention away from the Clintons and back to a sharp focus on the Obama-Biden ticket. Although he has been in the Senate since 1973 and run for president twice, Mr. Biden will also seek to introduce himself to an audience that knows little about him.

In accepting Mr. Obama’s invitation to join the ticket on Saturday, Mr. Biden characterized himself as the son of blue-collar America, an Irish-Catholic kid from Scranton, Pa., who has lived America’s story. As he does in many speeches, he will likely reprise the personal and political setbacks he has suffered and say that he learned as a boy that “it’s not how many times you get knocked down, it’s how quickly you get up.”

He will seeks to connect both himself and Mr. Obama to the larger narrative of American struggle and triumph and to appeal with the working-class, older, white Americans who flocked to Mrs. Clinton in the primaries and kept the contest close right up to the end of the primary calendar.

Mr. Biden, chairman of the Senate Foreign Relations Committee, is also expected to highlight his expertise on international matters, filling a gap in the young Mr. Obama’s relatively thin public policy resume.

Mr. Obama, who has been touring the battleground states of Wisconsin, Iowa, Missouri and Montana this week, is set to arrive in Denver about 6 p.m. and will probably appear on stage with Mr. Biden at the end of his remarks, which begin at about 8:30 p.m. local time.

The convention moves from the Pepsi Center to the 70,000-seat Invesco Field for Thursday night’s acceptance speech by Senator Obama. Former Vice President Al Gore will speak before him.

The Obama campaign announced Wednesday that after the convention ends, Mr. Obama and Mr. Biden will take a three-day bus tour of Pennsylvania, Ohio and Michigan, three states that Mr. Obama lost to Mrs. Clinton in the primaries and that will be heavily contested in the fall.