Denver - Senator Edward M. Kennedy, struggling with brain cancer, arrived on Monday night at the Democratic National Convention in a triumphant appearance that evoked 50 years of party history as Democrats gathered to nominate Senator Barack Obama for president.

    Mr. Kennedy's appearance wiped away, at least for the evening, some of the tension that continued to plague the party in the wake of the primary fight between Mr. Obama and Senator Hillary Rodham Clinton. It also represented an effort by the Obama campaign to claim the Kennedy mantle, and it set the stage for the second part of what was designed to be an emotionally powerful two-act evening: an appearance later by Michelle Obama, who began a weeklong effort to present her husband - and his entire family - as embodiments of the American dream.

    "You see, Barack doesn't care where you're from, or what your background is, or what party, if any, you belong to," said Mrs. Obama, without explicitly mentioning the racial undercurrents that have swirled around her husband's candidacy. "You see, that's just not how he sees the world. He knows that thread that connects us - our belief in America's promise, our commitment to our children's future - he knows that that thread is strong enough to hold us together as one nation even when we disagree."

    At the end of the evening's proceedings, Mr. Obama appeared before the convention by video hookup, with his young daughters, Malia and Sasha, joining his wife on stage for what was clearly intended to transmit a loving American family tableau.

    Even as Mrs. Obama led the effort to present a warm and positive portrayal of her husband during the portion of the proceedings broadcast by network television, Democrats moved aggressively earlier in the proceedings to portray his likely Republican opponent, Senator John McCain of Arizona, in harsh terms. In an early taste of coming efforts to define Mr. McCain negatively, they attacked him for his ties to President Bush, his opposition to abortion rights and as being out of touch with the concerns of ordinary Americans.

    "Republicans say John McCain has experience," said Representative Nancy Pelosi of California, the House speaker. "We say John McCain has the experience of being wrong."

    As elaborately choreographed as the evening was, with a series of speeches carefully screened by the Obama campaign, it was marked by an event that no was sure until the very last moment would happen, given the severity of Mr. Kennedy's illness. He arrived at the convention site here shortly before dusk, accompanied by a flock of family members. He walked a few halting steps to a waiting golf cart, which drove him into the arena.

    After a speech by his niece Caroline Kennedy and a video tribute, Mr. Kennedy walked slowly to the lectern, limping slightly, with his wife, Victoria, who kissed him and left him there. His white head of hair was noticeably thinned in the back; throughout the speech, he stared straight ahead to the front of the room. The crowd, many of them wiping tears from their eyes, cheered for close to two minutes until he settled them down.

    "My fellow Democrats, my fellow Americans, it is so wonderful to be here," said Mr. Kennedy, his voice booming across the hall. "And nothing - nothing - is going to keep me away from this special gathering tonight."

    A stool that had been slipped behind him went unused during his 10-minute speech. And while Mr. Kennedy spoke slowly and at times haltingly, his voice was firm and he was in command of this moment, gesturing and sounding very much like the man who enraptured the party's convention 28 years ago.

    "There is a new wave of change all around us," he said, "and if we set our compass true, we will reach our destination - not merely victory for our party, but renewal for our nation. And this November, the torch will be passed again to a new generation of Americans.

    "So with Barack Obama, and for you and for me, our country will be committed to his cause."

    In an invocation of his parting remarks to the 1980 convention, when he promised that "the dream will never die" as he ceded the presidential nomination to Jimmy Carter, Mr. Kennedy declared, "The work begins anew, the hope rises again, and the dream lives on."

    The Democrats' 2008 convention was gaveled to order with a procession of speakers - including a heavy representation of women and Hispanics - who began laying the foundation for what Mr. Obama and his advisers hope to accomplish over the next four days. Throughout the day, aides to Mrs. Clinton, of New York, and Mr. Obama, of Illinois, worked to ease tensions over the Clintons' roles at the convention. Mrs. Obama, in her speech, made a point of saluting Mrs. Clinton's achievements.

    Addressing the New York delegation earlier in the day, Mrs. Clinton strongly urged her supporters to vote for Mr. Obama at the convention. And Mr. Obama, campaigning in Davenport, Iowa, said he had spoken to former President Bill Clinton at length earlier in the week and made clear that he welcomed Mr. Clinton's role at the convention.

    Aides to Mr. Obama and Mrs. Clinton were working toward an agreement to start a roll-call vote with both of their names in nomination but to have her call for unanimous support for him.

    From the beginning, Democratic leaders from across the country were assailing Mr. McCain, in a way that made clear that the convention would not be a replay of the Democrats' genteel gathering in 2004.

    "John McCain has spent more than 25 years in Washington voting against women's freedom," said Nancy Keenan, the head of Naral Pro-Choice America, "and has pledged to appoint justices to the Supreme Court who will overturn Roe v. Wade."

    Senator Claire McCaskill of Missouri said: "Know that this son of a single mom will stand up for the dreams of our daughters. And I know that John McCain won't."

    But if some speakers took the rough road, a whole other roster of speakers - starting with old friends and associates of the Obamas and scheduled to culminate with Mrs. Obama's address - offered a warm and intimate picture of Mr. Obama and his family.

    If one big task for Mr. Obama this week is to try to paint a critical picture of Mr. McCain and his policies, another is to try to present a fuller portrait of Mr. Obama and push back against Republicans' efforts to paint him as culturally and politically distant from mainstream America.

    Mr. Obama's half-sister, Maya Soetoro-Ng, talked about growing up in a family with little money, raised by a mother who was "a sturdy woman and an eternal optimist who understood that parents are our first and best teachers."

    Mrs. Obama spoke of her own family's blue-collar past and spoke of her husband's life as "a great American story."

    "Barack and I were raised with so many of the same values," she added. "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.

    "And Barack and I set out to build lives guided by these values and pass them on to the next generation."

    Ms. Obama had come under fire from Republicans for saying, earlier this year when talking about her husband's campaign, that "for the first time in my adult life I am proud of my country." Her speech seemed intended to address that; she repeatedly spoke of her pride in America. "That is why I love this country," she said.

    Once Mrs. Obama finished her speech, her husband's face appeared on a video screen from the home of a white family in Kansas City, Mo. "Now you know why I asked her out so many times, even though she said no," he said. "You want a persistent president."

    "What city are you in Daddy?" interrupted Sasha, who is by now accustomed to late-night video conferences with her forever-traveling father.

    "I'm in Kansas City, sweetie," he responded. "I want you guys to look after Mommy. I'll see you guys!"

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    Reporting was contributed by Jeff Zeleny in Davenport, Iowa; Michael Cooper in Los Angeles; and John M. Broder, Janet Elder, Patrick Healy and Jeremy W. Peters in Denver.