Backers of Hillary Clinton cloud Obama show

DENVER (Reuters) - Democrats opened their national convention on Monday and a rift involving Hillary Clinton's resentful supporters threatened to rain on presidential hopeful Barack Obama's nominating parade.

Democratic Party chairman Howard Dean pounded a gavel to open the four-day convention that Democrats say Obama must use to unite the party, draw a sharp contrast with Republican rival John McCain and back up soaring oratory with a policy for leading the country.

Obama tried to assuage anxiety among some Democrats about a mild slide in opinion polls that has left him in a dead heat with McCain heading toward the November 4 election.

He said his nomination acceptance speech on Thursday would be "workmanlike," short on lofty words and long on policy details.

He also played down divisions with the former president and first lady.

"I am absolutely convinced that both Hillary Clinton and Bill Clinton understand the stakes," he told reporters in Moline, Illinois.

The day's agenda was focused on outlining Obama's personal story. In excerpts from her evening keynote speech, Obama's wife, Michelle Obama, seemed to want to dispel Republican criticism of Obama as an aloof celebrity.

"And in the end, after all that's happened these past 19 months, the Barack Obama I know today is the same man I fell in love with 19 years ago," she said.

Michelle Obama also tried to cast her own personality in a popular glow.

"I come here as a wife who loves my husband and believes he will be an extraordinary president. I come here as a mom whose girls are the heart of my heart and the center of my world," she said.

Democrats hoped a tribute to Massachusetts Sen. Edward Kennedy, a symbol of Democratic liberalism who is battling brain cancer, would bring the party together. An aide to Kennedy said the senator would attend but not speak.

Casting a cloud over the convention was ongoing resentment from supporters of New York Sen. Clinton, miffed that she lost the nomination and upset that she was not picked as Obama's vice presidential running mate. Obama chose veteran Delaware Sen. Joe Biden, who arrived at the convention on Monday.

Clinton, speaking to sign-waving supporters from her home state delegation before the convention began, urged party unity.

"We are after all Democrats, so it may take a while," she said. "We're not the fall-in-line party. We are diverse. But make no mistake, we are unified," she said.

IN AGREEMENT ON SPEECHES

Negotiators from the Clinton and Obama camps came up with a plan to placate Clinton supporters by allowing three speeches on behalf of a symbolic nomination for Clinton before the floor turns to nominating Obama as the Democratic candidate.

Amid reports that former President Bill Clinton was upset that he was asked to speak about foreign policy on Wednesday night instead of the U.S. economy, Obama told reporters traveling with him that he had told Clinton in a phone conversation last week he could talk about whatever he wanted.

"I said, Mr. President, you can say whatever you like. Bill Clinton is a unique figure in our politics," Obama said.

A new opinion poll showed how much work lay ahead to rally Clinton supporters behind him. The CNN/Opinion Research Corp. poll said the race between Obama and McCain was even, each with 47 percent support.

It said 66 percent of Clinton supporters backed Obama, down from 75 percent at the end of June. Twenty-seven percent of them said they would support McCain in the November 4 election, up from 16 percent in late June.

On the convention floor, Eufaula Frazier, a retired school teacher and a Democratic delegate from Florida, wore her "Hillary for president" campaign button but said she is ready to vote for Obama.

"There may be a few of us who go for McCain, but most of us understand we need to kick Republicans out of the White House," Frazier said.

Republicans who established a "war room" in Denver sought to sow discord by staging a news conference with a former Clinton backer who now backs McCain.

The McCain campaign has sought to exploit the Democratic divide. Senior McCain aide Carly Fiorina said disgruntled women supporters of Hillary Clinton "want a leader whose judgment and experience they can trust."

(Additional reporting by John Whitesides, Caren Bohan, Thomas Ferraro and Rob Doherty; Editing by Howard Goller and David Wiessler)