John F. Kerry staked his hopes for the White House Thursday night on a gamble that would have seemed almost unimaginable for a Democrat not so long ago, challenging President Bush to a debate on the twin pillars of Republican success: values and security.

It is a challenge that has been building steadily along the campaign trail all year, as Kerry and his advisers confronted the political realities of the first presidential campaign since Sept. 11, 2001, and later the aggressive effort by the Bush team to define the Democrat as outside of the political mainstream.

Before a jam-packed audience at FleetCenter, Kerry delivered an acceptance speech designed not just to promote his candidacy but also to answer critics who say he is too liberal, too cerebral and lacks an obvious sense of humor.

But at its heart, it was an attempt to turn the policies of the Bush administration on their head and argue in often toughly worded language that there is a different way to keep the country safe, a better way to make it prosperous, and a less divisive way to govern.

"I will be a commander in chief who will never mislead us into war," he said. "I will have a vice president who will not conduct secret meetings with polluters to rewrite our environmental laws. I will have a secretary of defense who will listen to the advice of our military leaders. And I will appoint an attorney general who upholds the Constitution of the United States."

There were notable omissions in Kerry's speech, however, that raise questions about the course he and his party have chosen for the campaign. Like other speakers during the four nights of the convention, Kerry only briefly touched on Iraq, the issue that has shaped and dominated this presidential campaign, divided the Democratic Party and at times bedeviled his own candidacy. At a time when many Americans are looking for an exit strategy and may wonder whether Kerry has a plan for Iraq that is different from Bush's, he offered only the assurance that he knows how to get it right.

Nor did Kerry or running mate John Edwards use their speeches this week to confront their opponents directly or persuasively argue the case for turning out the administration. His advisers believe the public already is looking to replace Bush and needs only to find a level of comfort with Kerry to change presidents. They may be correct, but that too is a gamble, for there will be no better opportunity to make that case before the fall debates.

Rarely has an acceptance speech at a political convention come with so much hype and drama -- as well as nervousness within a candidate's own party about his capacity to rise to the moment. Even Kerry's closest allies recognized that after 18 months on the campaign trail, he remains an incomplete portrait to many voters.

For all his attributes, Kerry has never been known as a charismatic politician and rarely has he demonstrated a great gift for political oratory. His acceptance speech is not likely to change that reputation. He tried to make himself more human and more appealing, with memories of his parents, stories of his childhood and references to his wife and children. Ultimately, however, he appeared willing to cede the battle over personality and likeability to Bush, believing those may be less significant in the minds of voters than they were four years ago.

Instead, he framed his candidacy around attributes that he and his advisers believe will be more relevant , suggesting that in a dangerous world, seriousness and an appreciation of the complexities of issues are their own virtues and that, if he is not always the warmest of politicians, he has a lifetime of experience that should reassure voters.

All week the convention program was shaped with a single aim, to project Kerry and the Democratic Party as committed to the nation's security. On Thursday night, the Massachusetts senator cited his combat record as a naval officer in the Vietnam War to assure his national television audience that they can trust the Democrats in the war on terrorism. "I defended this country as a young man, and I will defend it as president," he said.

Kerry reached for every experience in his biography to associate himself with symbols of strength and patriotism, invoking a tattered and bullet-ridden flag that waved at the back of his Swift boat in Vietnam and the imagery of a young solider on patrol to suggest that the lessons he learned 35 years ago uniquely equip him to become president today. "As president," he said, "I will wage this war with the lessons I learned in war."

He invoked the flag to challenge the Republicans on values, an area of political debate where Democrats have consistently been on the defensive in recent years. As with security, Kerry sought to demonstrate that Republicans have taken the wrong road. But the core of his argument was that the values championed by Republicans divide the country while the values he promotes would lift up the country.

He talked about his own faith to dispel the image of the Democrats as a party hostile to religion, but he said that, unlike some other politicians, "I don't wear my religion on my sleeve." Faith, he said, had infused him with the kind of values -- economic justice, taking care of the elderly by preserving Social Security, protecting the environment and educating children -- that Democrats have long championed.

Kerry's emphasis on redefining the values debate signaled to Democrats that he would not shrink from the GOP attacks the way Michael S. Dukakis did in 1988, and one of his biggest applause lines came when he challenged Bush not to use the Constitution for political purposes, a reference to the president's call for an amendment to bar same-sex marriage. But he otherwise avoided any direct discussion of the kinds of social issues that have long put the Democrats on the defensive, from gay rights to gun rights. No matter what he does to try to change the debate, he will find Republicans eager to challenge him on these issues.

Kerry's advisers said they would use the convention to reach out to undecided voters, and in his speech, Kerry appealed directly to those voters with a call for a campaign of big ideas and not, as he put it, small-minded attacks. He challenged Bush to "build unity in the American family, not angry division," and he said that if elected he will fill his administration not just with Democrats but with Republicans as well.

Throughout the speech, Kerry mixed criticism of the administration with efforts to portray himself and his party as optimists with a positive message. He was both partisan and bipartisan, casting the Republicans as out of the mainstream while calling for a restoration of civility to the political debate. He praised Bush for his conduct in the days immediately after Sept. 11, but used that praise to cast into question much of what Bush has done since.

"I am proud that after September 11th all our people rallied to President Bush's call for unity to meet the danger," he said. "There were no Democrats. There were no Republicans. There were only Americans. How we wish it had stayed that way."

Almost in the next breath he suggested that Bush had evaded and equivocated on fixing the nation's intelligence capabilities, accused the president of bringing about a loss of respect for the United States in the world and suggested that, without a change of administrations, there is little hope of attracting military and financial support for the mission to secure Iraq.

"We need a president who has the credibility to bring our allies to our side and share the burden, reduce the cost to American taxpayers and reduce the risk to American soldiers," he said. "That's the right way to get the job done and bring our troops home. Here is the reality: That won't happen until we have a president who restores America's respect and leadership, so we don't have to go it alone in the world."

The long domestic agenda Kerry outlined Thursday night included familiar elements: expanded access to health care, energy independence, a pledge to create good jobs and take away incentives for companies to ship jobs overseas. And in presenting that agenda, he stole a line from the 2000 Republican convention when he declared repeatedly, "Help is on the way."

Still unanswered is how Kerry plans to keep all his promises for new programs and tax cuts and still meet his pledge to cut the soaring deficit in half in four years.

Kerry's speech was short on soaring rhetoric, one big organizing idea or the kind of phrase that can encapsulate an entire candidacy. It was instead an effort to illuminate the senator's biography, to demonstrate the values he has brought to public service and to signal that he will fight to win the presidency.

But the speech demonstrated the journey Democrats have followed since the 2002 campaign, when they were reluctant to talk about national security because of what they perceived as Bush's strength on the subject. Kerry's gamble is that there is no other way to win the presidency than to show that the Democrats have adapted to the challenges of an era of terrorism.

Even before the speech, Democrats said their convention had accomplished many of the goals they had set out for the week, from showing a united face to the country to offering voters a positive and hopeful tone. The question that remains even after Kerry's acceptance speech is whether voters who tuned in saw a strong potential president but also an uplifting and compelling vision for a Kerry presidency.

Researcher Lucy Shackelford contributed to this report.

Before his acceptance speech, John F. Kerry embraced his former Swift boat crewmates onstage. "I am John Kerry, and I am reporting for duty," he said.The nominee's daughters, Alexandra, left, and Vanessa, take the stage. "When he loves you -- as he loves me and my sister and his family, as he loves the men who fought beside him -- there is no sacrifice too great," Alexandra Kerry said of her father.A delegate adorned with symbols of party loyalty listens during the final session at Boston's FleetCenter.