Washington - With Democrat Barack Obama losing ground steadily in opinion surveys against his Republican rival for the White House and facing criticism for his star power, the last thing Obama would seem to need is a star-studded Democratic Convention.

Yet talk-show host Oprah Winfrey, singer Kanye West and actor Ben Affleck are all expected to be in Denver, Colorado, for the presidential nominating spree that opens Monday.

They are part of the sideshow the US public has come to expect of the centre-left Democrats when they meet every four years to formally nominate their presidential candidate.

Senator Obama's plans to speak Saturday in Springfield, the Illinois state capital where he got his start in politics, have added to anticipation before the convention begins. There is speculation he could even reveal his long-awaited vice presidential choice at the event.

But as the orchestrated, dramatic run-up to the Democratic gathering built, it was clear by Wednesday that John McCain, the presumptive Republican nominee, has cut considerably into Obama's lead in most nationwide polls, bringing the presidential race to a dead heat.

The presence of such star power in Denver could give another opening for McCain to jab at his opponent for being the "greatest celebrity in the world" - a phrase McCain used in television ads to dismiss the 200,000 people who flocked to Obama's speech in Berlin last month and question the Democrat's experience.

Any concerns by the Obama campaign over another round of such battering have not deterred plans by the Recording Industry of America Association (RIAA) to invite Democratic members of Congress and other party stalwarts to its bash next Wednesday night in Denver.

The biggest star will be hip-hop king Kanye West. The RIAA emphasized that the party will support U2 frontman Bono's anti- poverty One Campaign.

The RIAA is throwing a similar gala the following week at the Republican Convention in St Paul, Minnesota, starring Chris Daughtry of American Idol fame, the Washington Post reported. That could take some of the wind out of McCain's anti-celebrity sails.

Either way, the RIAA was intent on emphasizing the anti-poverty angle of the gatherings because of questions being raised about the ethics of such extravagant entertainment by an industry group, media reports said.

Just last year, Democrats spearheaded new rules to block lavish parties for Congress members at national political conventions, the Wall Street Journal noted.

But charitable fundraisers are exempted under new rules, meaning the RIAA's celebrity bash is apparently OK because it benefits an anti-poverty cause, the Journal reported.

US actor Ben Affleck's appearance at a Poker Players Alliance tournament was also seen as acceptable because winnings are being donated to the Paralyzed Veterans of America.

All of this this may seem to have little to do with nominating the US presidential candidates - decisions that were already made by Democratic and Republican party loyalists in state-by-state primary voting that ended in June.

But nominating conventions have evolved into political theatre that aims to re-introduce candidates to the public before the November 4 elections and project a show of unity after often bitter exchanges during the primaries' scramble.

That means that another celebrity, talk show diva Oprah Winfrey, will be playing a lower profile than expected next week in Denver, the Los Angeles Times reported, citing Oprah friend and employee Gayle King.

Many of Oprah's female fans apparently disagreed with her campaigning for Obama instead of Senator Hillary Clinton, who narrowly lost her bid for the Democratic nomination, the Times reported. Oprah's show apparently suffered in popularity afterwards, the newspaper reported.

While Oprah will keep her head low, Clinton, after much debate within the Obama campaign, was given a large role as the convention's headline speaker on Tuesday evening.

The former first lady will even claim the spotlight during a state-by-state roll call vote initially opposed by Obama.

Clinton's 1,800 or more delegates and tens of thousands of campaign volunteers insisted the Democratic Party luminary be recognized for her achievement as a woman who went further than any other woman in US history in seeking the White House.

Clinton's strong role at the convention is expected to cement her own political star power as Democrats launch their bid to reclaim the White House on November 4.