With only two weeks left before Democrats meet in Colorado to nominate Barack Obama, much of the debate this week has been on what Hillary and Bill Clinton will do during the August 25-28 party unity event in Denver.

Late Thursday, it appeared that former president Bill Clinton, one of the Democratic Party's most important figures, has been invited by Obama to be a lead speaker on August 27, the evening before Obama accepts the nomination, media reports said.

But that still hasn't resolved the question of what to do about Obama's ousted rival for the nomination, the former first lady, and her disgruntled supporters, even as she heads to Nevada on Friday to campaign for him.

And Obama still hasn't declared his vice presidential candidate, teasing hopes among her supporters.

It's unusual for so much to be left up in the air this near to the convention. Traditionally, a candidate has sealed the nomination by April or May, and spends the summer raising money and consolidating the party base. There's a break in campaign rhetoric until September.

But this year's all-out scramble for the Democratic presidential nod has broken all records. The final outcome went into June. The party is poised to nominate the country's first African-American candidate of a major political party, after he narrowly beat the first woman candidate for the same honour.

Obama, 47, has been intensely engaged in a daily exchange of campaign barbs with Republican nominee-designate Senator John McCain.

Now, there's the Clinton issue again.

Clinton, 60, is caught between demands by her supporters that she put her name up for nomination for a formal round of recognition of her historic candidacy and Obama's need to keep the limelight on him.

By all accounts, although no formal announcement had been made, it appeared that the Obama campaign was prepared to offer Hillary the keynote speaker honour for August 26, the 88th anniversary of the passage of the right-to-vote for women.

In exchange, Clinton was expected to keep her name out of the state-by-state roll call, party insiders said.

By Thursday, however, an unauthorized film clip of Clinton speaking to supporters in California surfaced. She suggests that if she put her name in for nomination and a roll call vote, the party would "come out stronger if people believe that their voices were heard."

"That is a very big part of how we come out unified. People want to feel like - OK, it's a catharsis. We're here, we did it, and everybody get behind Sen. Obama."

Obama dismissed the idea of "catharsis."

"I don't think we're looking for catharsis. I think we're looking for energy and excitement about the prospect of change in this country," he told reporters on board his campaign plane.

A show of party unity is vital for centre-left Democrats to get the all-important bounce out of the convention and toward the November 4 general elections.

Clinton's supporters note that she has already withdrawn from the race and thrown her support behind Obama, and see no harm in formal recognition.

In the past, such candidates as Senator Edward Kennedy - who is suffering from brain cancer and will deliver a videotaped message Monday night at the convention - and civil rights activist Jesse Jackson were named in the roll call vote.

Party officials are uneasy over the number of Clinton supporters who have vowed not to vote for Obama. One group calls themselves "18 Million Voices Rise Hillary Rise" - a reference to the poetic endorsement by African-American poet Maya Angelou and the 18 million people who voted for Clinton in the primaries - plans a parade and rally in Denver on August 26 to celebrate Clinton's accomplishments.

Mary Boergers, a Maryland state senator and Clinton delegate, said a number of fellow Clinton delegates were thinking about a protest vote during the state roll call vote.

"If they don't allow us by the rules to vote for Hillary, we will vote 'present'," she said in an interview.

For Boergers, the prospect of not being able to declare "yes" for the first woman to come so near to a presidential nomination is "greatly" distressing.

"It diminishes really the value of all of these primaries and all of these caucuses. It makes the convention a coronation and makes the convention really meaningless," she said.

According to a recent poll, most of Clinton's women supporters have come to terms with her defeat and her absence from the Obama ticket. Only 18 per cent say they will not vote for Obama, considerably fewer than right after the final primary in June.

But the poll also showed that women hold an important key to winning the elections, because neither Obama nor McCain has yet won a majority of women voters into their corner.