DENVER — After an emotional speech by an ailing Sen. Edward M. Ken-nedy, the face of the Democratic Party shifted last night to a new generation of leaders as Michelle Obama opened the Democratic National Convention with a tribute to her husband and a call to the country to listen "to our hopes instead of our fears," and "to stop doubting and to start dreaming."

Seeking to ground Sen. Barack Obama in the experience of America's working class while recapturing the lofty ideals that propelled him toward the Democratic presidential nomination, Michelle Obama's family-themed speech was the climax of a dramatic opening day for a political party confident of its chances of capturing the White House but still struggling to lay aside its own divisions.

A weak economy and a war in Iraq now in its sixth year have offered Democrats and their young candidate an ideal political environment in which to push for widespread change. But Obama has yet to close the deal with the electorate, or even some of the Democrats who backed his primary opponent, Sen. Hillary Rodham Clinton of New York.

But once the curtain raised on Denver's raucous Pepsi Center, the party appeared poised to come together. The delegates cheered every mention of Clinton and gave the same treatment to Obama's running mate, Sen. Joseph R. Biden Jr. of Delaware, and the party's 2004 nominee, Sen. John F. Kerry of Massachusetts. Kennedy, who has a brain tumor but appeared spry in a surprise appearance, offered a poignant moment of reflection on the last time a youthful Democrat won the White House. To thunderous applause, he promised to be present in the Senate in January to greet a new Democratic president.

"The work begins anew. The hope rises again, and the dream lives on," he said, echoing his speech from the 1980 Democratic convention in which he was denied the party's nomination.

Michelle Obama also did her part to try to heal the lingering wounds of the long struggle for the nomination when she recognized Clinton, "who put those 18 million cracks in the glass ceiling, so that our daughters — and our sons — can dream a little bigger and aim a little higher."

But the stream of new faces — including Michelle Obama's brother, Craig Robinson, and freshman Sen. Claire McCaskill of Missouri, one of the candidate's fiercest supporters — and a rousing anthem from John Legend, who helped craft the viral music videos that have powered the Obama movement — signaled the torch was changing hands. Caroline Kennedy tried to bridge that generational shift when she told the crowd, "I have never had someone inspire me the way people tell me my father inspired them, but I do now: Barack Obama."

When Michelle Obama took to the podium, she was greeted with sustained applause and a sea of blue "Michelle" placards.

"Barack doesn't care where you're from, or what your background is, or what party — if any — you belong to. That's not how he sees the world," she said. "He knows that thread that connects us — our belief in America's promise, our commitment to our children's future — is strong enough to hold us together as one nation."

After she finished, daughters Malia, 10, and Sasha, 7, met her on stage, where they were soon joined by her husband via a video link from Kansas City, Mo., where he watched the speech at the home of Jim and Alicia Girardeau. "You were unbelievable," he said, "and you look pretty cute," to which Sasha replied, "Thanks."

Campaigning in Iowa yesterday, Obama tried to ease his party's divisions, conceding that "there are going to be some of Sen. Clinton's supporters who we're going to have to work hard to persuade to come on board — that's not surprising." But, he added, "if you take a look this week, I am absolutely convinced that both Hillary Clinton and Bill Clinton understand the stakes."

But the nerves were not easily calmed ahead of Hillary Clinton's speech today and former President Bill Clinton's appearance tomorrow. Hillary Clinton addressed the New York delegation at a breakfast in the morning.

"We were not all on the same side as Democrats, but we are now," she said. "We are united and we are together and we are determined."

Clinton is expected to release her delegates to Obama today, a symbolic gesture that reduces the prospects for major disruptions when the roll is called to nominate the senator from Illinois, a historic moment when Obama will become the first black politician to head a major party's national ticket.

Meanwhile, federal authorities are looking into reports that a man arrested with rifles, ammunition and drugs in his truck may have made threats against Barack Obama, officials said yesterday.

Two other men were arrested in the case.

"It's premature to say that it was a valid threat or that these folks have the ability to carry it out," said a U.S. government official familiar with the investigation.

Tharin Gartrell, 28, was arrested during a traffic stop early Sunday by police in the eastern Denver suburb of Aurora. In his truck, officers found two rifles, including one with a scope; a bulletproof vest; boxes of ammunition; walkie-talkies; and suspected narcotics, said Aurora police Detective Marcus Dudley.

Police alerted federal authorities, who soon arrested Nathan Johnson, 32, at a hotel in Denver, Dudley said. A third man, Shawn Robert Adolf, 33, was arrested at a suburban Glendale hotel, Dudley said.

The Associated Press contributed to this report.