DENVER - On the eve of the Democratic National Convention, Barack Obama said Sunday he hoped a week of political speechmaking would persuade reluctant middle-class voters to swing behind his bid for the White House, while Republicans sought to stir discontent among Hillary Rodham Clinton's supporters.

Clinton was having none of it. In a gesture of unity, Obama's rival in the bruising battle for the nomination was expected to release the delegates she won in primaries and caucuses, telling them in midweek they are now free to join her in supporting the victor.

Obama, bidding to become the first black president, campaigned through swing-state Wisconsin, then flew home to Chicago to work on the acceptance speech he will deliver before 75,000 partisans on the convention's closing night.

Previewing the week ahead, he said he hoped convention viewers would conclude, "He's sort of like us. He comes from a middle-class background, went to school on scholarships. He and his wife had to figure out child care and how to start a college fund for their kids.'"

Clinton outpolled Obama among working-class voters in many states through the winter and spring, and Sen. John McCain and the Republicans have worked relentlessly in more recent weeks to depict the Illinois senator as an elitist who is out of touch with blue-collar concerns.

With Democrats descending on their highly fortified convention city, party officials worked energetically to assure a harmonious week.

Thousands of blue signs that read simply "Unity" were stockpiled inside the Pepsi Center for distribution to convention delegates at whatever moment Obama's high command deemed appropriate.

And on a unanimous vote, the party's credentials committee restored full voting rights to delegations from Florida and Michigan. Both states were stripped of their voting rights earlier in the year in retaliation for holding primaries before party rules allowed.

"The only way we will be successful is if we are unified as a party and all Democrats know we are full partners," said Chris Edley Jr., a member of the panel.

The Democrats were meeting with public opinion polls giving Obama a modest advantage at best in the race to become the nation's 44th president. McCain has been on the political offense in recent weeks, and he has successfully cut into what had been a slightly more comfortable lead for the Democrat.

If Democratic unity was uppermost in the minds of Obama's aides, McCain had other ideas.

The Republican presidential contender's campaign readied a television commercial — there was no immediate evidence it had been broadcast — suggesting Obama had snubbed Clinton when he picked Delaware Sen. Joseph Biden as his vice presidential running mate.

"She won millions of votes but isn't on the ticket. Why? For speaking the truth," says the ad, which also shows Clinton criticizing Obama during their protracted battle for the Democratic presidential nomination.

The former first lady has praised Biden's selection. In response to the ad, spokeswoman Kathleen Strand noted that Clinton "has said repeatedly that Barack Obama and she share a commitment to changing the direction of the country, getting us out of Iraq and expanding access to health care. John McCain doesn't. It's interesting how those remarks didn't make it into his ad."

The first arrests of the convention week were reported when about 1,000 anti-war demonstrators marched through downtown under the watchful eye of police in riot-control gear. Officials did not immediately provide details on the number of those taken into custody, or even confirm that those arrested had taken part in the march.

Inside the Pepsi Center, where the convention's opening gavel falls on Monday, the floor seating was rearranged to reflect a new political order. Delaware's delegates were granted a spot closer to the front, an upgrade resulting from Biden's selection as Obama's vice presidential running mate.

With McCain trying to use Clinton to divide the Democrats, Obama strongly defended his vice presidential choice, a selection that seemed designed to fill a gap in his own foreign policy resume while appealing to blue-collar voters.

"He's got the passion to lift up middle-class Americans, he hasn't forgotten his working-class roots, he has the expertise that will make him a great counselor on international crises that might come up," Obama told reporters before boarding his plane in Eau Claire, Wis.

The opening night convention program — featuring an appearance by Michelle Obama — was scripted to reach out to the same segment of the electorate. Officials said her remarks would present her husband — the son of a white mother from Kansas and a black father from Kenya who later left the family — as anything but elite.

Barack Obama's half-sister, Maya Soetoro-Ng, and Michelle Obama's older brother, Craig Robinson, also will have roles in the convention.

Clinton's address is the centerpiece of Tuesday's session, and given her appeal during the primaries, her remarks could prove pivotal to Obama's chances of success in the fall. A recent NBC-Wall Street Journal poll made clear how much work Obama has yet to do to appeal to her voters.

The survey indicated that only half of those who voted for Clinton are now supporting Obama, while about 20 percent are backing McCain.

Mindful of that, Obama agreed to allow Clinton's name to be placed in nomination on Wednesday night. The move may well reassure her supporters, but it risks at least the appearance of a divided party to viewers watching the proceedings at home on television.

Clinton's spokesman, Philippe Reines, said her meeting with her delegates this week will be an opportunity to "thank them for their hard work and support, and most importantly to encourage them to support and work for Senator Obama as strongly as she has in order to elect him in November."

Biden spent the day at home in Delaware after Saturday's campaign debut with Obama in Illinois.

Spokesman David Wade said the senator would remain on the ballot for a new Senate term this fall while running for national office. If Obama wins the White House, Biden would resign from Congress to become vice president, and the governor of Delaware would appoint a temporary replacement.