Some of pop music's biggest stars played and preached before tens of thousands of fans in Hyde Park here and at nine other sites across the globe Saturday in a coordinated campaign to pressure world leaders into committing billions of dollars in aid and debt relief for Africa.

Two million people turned out fo Live 8 concerts featuring 150 bands in sites as far-flung as Moscow and Johannesburg, Tokyo and Philadelphia, while millions more watched on television, listened on radio, or took in webcasts on America Online. They all heard one message: that the richest nations can and should do what is needed to end poverty and human suffering in the world's poorest continent.

Rock-and-roll has seldom been louder, more self-important, more demanding or, at times, more sanctimonious. Here in London, where the flagship concert was held, A-list performers ranging from Paul McCartney to U2 to Elton John to REM to Coldplay to Madonna delivered a mix of pop anthems and mini-sermonettes, while the big screens behind them alternated scenes of starving babies and desperate mothers with slogans such as "Make Poverty History."

The master of ceremonies was Bob Geldof -- "Saint Bob" as he's known to friends and critics alike -- the Irish rock star who masterminded "Live Aid," the first pop global charity extravaganza 20 years ago to raise money for famine victims in Ethiopia. This time around, Geldof told the crowd, the goal was to raise consciousness, not cash, to put the pressure on the Group of Eight -- the world's wealthiest countries, whose leaders are holding their annual summit starting Wednesday in Edinburgh.

"Eight men in one room can change the world," Geldof told the roaring crowd.

Bono, the lead singer for U2 who has been the other driving force behind the Live 8 effort, told the audience: "This is our moment, this is our time, this is our chance to stand up for what is right.

"We are not looking for charity, we are looking for justice."

Thousands were also looking for a good time. Nadia Kadoaz, 30, arrived early this morning with two friends from Dusseldorf, Germany, after an all-night bus and ferry ride. They planned to begin the return journey this evening as soon as the show ended. "We're young, after all," said Kadoaz, who said they had come for the music, not the message.

Paul Carlile, 50, a London businessman, said he was here for "a bit of both, really. I think this will show that the public has influence on the world stage. It will add to the consciousness of the whole thing."

Some 150,000 tickets had gone quickly, and the organizers handed out an additional 55,000 free tickets for those willing to watch the show on a big screen out of range of the stage. Still, dozens of scalpers sought to cash in.

One sidled up to Helga Riehen, who had flown in from Hamburg, Germany, on Friday night and carried a hand-lettered "Need Ticket" sign as she waited hopefully outside the VIP gate. He offered her a ticket for 600 pounds -- around $1,100. She shook her head in disbelief.

"I'm just a normal person," said Riehen, who works for a car rental agency back home. "I just came to hear the bands."

Known for his self-righteousness and self-deprecation, Geldof is a cantankerous and controversial figure here who was knighted for his work in raising funds for Ethiopia. Critics have contended that while the Live Aid concerts made Westerners feel compassionate, they did little to alleviate long-term suffering.

This time around Geldof and Bono have allied themselves with Tony Blair and Gordon Brown -- Britain's prime minister and finance secretary respectively -- to push a three-pronged program that includes wiping out debt payments for poor nations, doubling international aid and eliminating trade barriers that restrict Africans from selling their products abroad. Blair and Brown say they are working to compel fellow leaders to adopt the plan at the summit.

Some critics argue that Geldof and Bono have underestimated both the extent of Africa's problems and the ability and willingness of Western leaders to do something about them. More aid, for example, if misdirected or misused, could compound the continent's poverty.

"They appear to believe that a consensus can be achieved between the powerful and the powerless, that they can assemble a great global chorus of rich and poor to sing from the same sheet," wrote globalization critic George Monbiot in the Guardian here. "They do not seem to understand that, while the G8 maintains its grip on the instruments of global governance, a shared anthem of peace and love is about as meaningful as the old Coca-Cola ad."

Geldof also came under fire for signing up a collection of mainstream, middle-aged and mostly white pop acts for the main show here in Hyde Park and for suggesting that the stars avoid criticizing leaders such as President Bush at the concerts. At the last minute a smaller concert featuring African and other black acts was organized for the Eden Project in Cornwall in southwest England. The only African performer at Hyde Park was Senegalese singer Youssou N'Dour.

Geldof also managed to anger a few of his international collaborators. He accused Italy of being "the most miserly of the rich countries" in a newspaper interview, while he chided Canadian Prime Minister Paul Martin for failing to fulfill a pledge to dedicate 0.7 percent of its gross domestic product to foreign aid. If Canada failed to do so, Geldof warned, it would give the United States an excuse to "simply hide behind the moral shadow of its smaller neighbor."

Still, no one contested the extent of Geldof's energy or commitment. Paul McCartney and Madonna were among the many who said they had felt compelled to appear because of Geldof's dogged insistence. Nelson Mandela, Kofi Annan, Bill Gates and Brad Pitt all showed up here or in Johannesburg to introduce music acts, demonstrating the mind-boggling breadth of Geldof's influence.

Chris Martin, leader of Coldplay (and husband of actress Gwyneth Paltrow), praised Geldof's campaign as "the greatest thing that's ever been organized probably in the history of the world" and said those who were cynical about it "are stupid."

Geldof presented his own human response to critics -- a radiant 24-year-old Birhan Woldu, one of the starving children featured in the original Live Aid concert, who briefly addressed the crowd. Geldof said her life had been saved by the money contributed 20 years ago. "Don't let them tell us that this stuff doesn't work," he told the crowd. "Here's this beautiful woman."

The day kicked off in Tokyo, where 10,000 watched Japanese act Rize, followed by Bjork, McFly and Good Charlotte. Johannesburg soon followed, along with Moscow, Paris, Rome and Berlin, where Green Day, Roxy Music and Brian Wilson headed the bill.

In London the show began with McCartney and U2 performing "Sgt. Pepper's Lonely Hearts Club Band." Act after act did tight three-song sets, including the first live performance of Pink Floyd's Roger Waters and David Gilmour since 1981. Sting delivered an updated version of the menacing "Every Breath You Take" while photos of the G8 leaders flashed on the screen.

While stars like Dido and Annie Lennox couldn't stop themselves from preaching, others went about their business with cool efficiency and few comments. Younger British groups like the Stereophonics and Razorlight produced blistering sets of hard rock, as did veteran U.S. band REM, whose leader Michael Stipe, sporting a dark gray suit and blue face paint, pranced around the stage like a deranged corporate executive.

But in the end it was a pair of oldsters -- Pete Townsend and Roger Daltrey of the Who -- who added a final skeptical note to an event that combined music, politics, spirituality and pomposity in one heady and confusing mix. The legendary rockers -- combined age 121 -- unleashed an incendiary version of "Won't Get Fooled Again,"a song that for 34 years has instructed listeners to view their leaders, whether politicians or rock stars, with extreme caution.

They can't say they weren't warned.

Staff writer Doug Struck in Toronto contributed to this report.

London calling: Snoop Dogg and REM's blue man Michael Stipe; Madonna with Birhan Woldu, now 24, one of the starving children featured in the original Live Aid concert; and Bono, above.Elton John, just one of many honky cats who played Hyde Park.