DENVER -- Ailing and aging, Sen. Edward M. Kennedy issued a ringing summons to fellow Democrats to rally behind Barack Obama's pioneering quest for the White House Monday night in a poignant opening to a party convention in search of unity for the fall campaign.

Democrats opened their four-day convention in the shadow of the Rocky Mountains as polls underscored the closeness of the race with Republican John McCain. And there was no underestimating the challenges confronting Obama, although he moved to head off a divisive roll call later in the week.

Under an emerging agreement with Hillary Rodham Clinton, it appeared likely both their names would be placed in nomination, and the former first lady would eventually call for his nomination by acclamation.

Besides lingering bad feelings from the Democratic primaries, he also faces alternately mocking and searing attack ads from McCain and his Republican allies, and a reminder that racism, too, could play a role.

"There are people who are not going to vote for him because he's black," said James Hoffa, president of the Teamsters union. "And we've got to hope that we can educate people to put aside their racism and to put their own interests No. 1." He spoke in an Associated Press interview.

Kennedy and Obama's wife were the bookends of an evening that left the delegates cheering, one representing the party's past, the other its present.

"The work begins anew, the hope rises again and the dream lives on," Kennedy said in a strong voice, reprising the final line of a memorable 1980 speech that brought a different convention to its feet. The senator has been undergoing treatment for a malignant brain tumor.

Obama's wife, eager to counter a Republican claim that her husband is an elitist, said his story is classically American, his family one that scrimped and saved "so he could have opportunities they never had themselves." Obama was largely raised by grandparents after his parents, a white woman from Kansas and a black man from Kenya, divorced.

Among his values, she said: "that you work hard for what you want in life, that your word is your bond and you do what you say you're going to do, that you treat people with dignity and respect, even if you don't know them, and even if you don't agree with them."

She shared a post-speech embrace on the podium with daughters Malia, 10 and Sasha 7. Moments later, Obama appeared via satellite from Missouri, praising her speech and drawing cheers from delegates.

The convention's opening gavel fell with Obama and Clinton still struggling to work out the choreography for the formal roll call of the states that will make him the party nominee.

Michelle Obama included a tribute to her husband's former rival, crediting her with having placed "18 million cracks in the glass ceiling" that constrains women's ambitions.

"There is no doubt in anyone's mind that this is Barack Obama's convention," Clinton told reporters early in the day. And yet, she said, some of her delegates "feel an obligation to the people who sent them here" and would vote for her.

Kennedy's speech was an implicit appeal to her delegates -- and the 18 million voters who supported her in the primaries -- to swing behind Obama.

He said the country can meet its challenges with Obama as president. "Yes we can, yes we will," he said, echoing Obama's own signature refrain.

In one of their first orders of business, delegates ratified a party platform tailored to Obama's specifications. It backs "complete redeployment within 16 months from Iraq," as well as health care for all, a new economic stimulus package and higher taxes on families earning over $250,000 a year.

"The Democratic Party strongly and unequivocally supports Roe v. Wade and a woman's right to choose a safe and legal abortion, regardless of ability to pay, and we oppose any and all efforts to weaken or undermine that right," it said.

As the delegates took their seats in the Pepsi Center, Obama campaigned in Iowa, the first in a string of swing states he is visiting en route to Colorado.

Obama delivers his acceptance speech on Thursday at a football stadium, before a crowd likely to total 75,000 or more. Then he and Sen. Joseph Biden of Delaware, his vice presidential running mate, depart for the fall campaign.

If the opening night's convention program had a feel-good quality, not so the intensifying campaign outside the hall.

Obama struggled to quash a television commercial financed by an independent Republican group that linked him to a 1960s-era radical -- before it could damage his candidacy as the infamous Swift Boat ads helped sink John Kerry four years ago.

He also shipped a new commercial that used humor to depict McCain as an extension of the Bush administration, the latest in a series of negative advertisements by both sides.

"Really can't explain the price of gas, or what has happened to the middle class," the announcer sings to the tune of Sam Cooke's "Wonderful World." With McCain and Bush appearing together on the screen, the announcer says, "Do we really want four more years of the same old tune?"

Howard Dean, the party chairman, rapped the opening gavel precisely on schedule at 3 p.m. Mountain Time -- before only a smattering of delegates.

"We are ready to compete in all 50 states in November," he said, even though Obama has already written off large portions of the South and Mountain West.

Schumer and Van Hollen said only a small fraction of Clinton's delegates remained unreconciled to Obama's triumph in the bruising primaries of the winter and spring.

Perhaps so, but they were vocal about it, and officials said one of the issues under discussion was whether to permit a noisy floor demonstration by Clinton's supporters when the former first lady's name is placed in nomination on Wednesday night.

Kathleen Kennedy Townsend, the eldest child of the late Robert F. Kennedy and a former lieutenant governor of Maryland, said the animosity that some Clinton delegates feel toward Obama is worsening. "There's a moment that you want to enjoy your bitterness," she said, although she emphasized that she is supporting Obama.