UNITED NATIONS — Members of the Black Eyed Peas performed, Bill Gates donated money, and Mayor Bloomberg hosted a party for world leaders, all in the name of eradicating half of the world’s poverty by the middle of the next decade. But as leaders from the wealthy countries kept a wary eye on the financial markets, some said it was unrealistic — unfair even — to ask them to funnel money to the poor during a financial crisis.

Having dedicated this year’s U.N. General Assembly session to fighting world poverty, Secretary-General Ban yesterday gathered heads of state, businesspeople, and cultural icons at the United Nations. Mr. Bloomberg hosted an event for heads of state, launching a campaign to combat poverty alongside Prime Minister Brown of Britain. President Mugabe, who was at the United Nations for the first time since Zimbabwe’s disputed elections this spring, demanded an increase in Western aid to poor countries.

Two members of the Black Eyed Peas, will.i.am and apl.de.ap, kicked off a star-studded U.N. event yesterday featuring the model Elle Macpherson, actress Kristin Davis, and Queen Rania of Jordan. “It’s calling individuals to realize their power in solving global poverty and ending world hunger,” will.i.am sang. “Enforcing the politicians to keep what they promised and picking the world leaders that will lead the world honest.”

But some leaders voiced skepticism. Right now, Foreign Minister Bernard Kouchner of France said, the financial crisis is confined mostly to America and Britain, while “Europe is protected. But for how long?” Speaking at a breakfast meeting with reporters yesterday, he added, “The talk about the millennium goals at a time of crisis is unfair.”

Mr. Brown, who has led a campaign in his country to promote the U.N. program known as the Millennium Development Goals, spent more time on the financial crisis since his arrival in New York on Wednesday than he had planned. Nevertheless, he said that giving up on the goals, known as MDGs, would be the “wrong answer.”

Mr. Brown, a former chancellor of the exchequer, gathered seven heads of state — including those from key economic leaders such as Brazil, Australia, and Spain — to discuss ways to combat the banking crisis and related global economic hardships.

The British premier plans to fly to Washington on Friday for a meeting with President Bush. Yesterday, he met with several managers of large Wall Street funds to study details of the crisis here, according to aides.

Mr. Brown also conducted a press conference alongside the president of the World Bank, Robert Zoellick, and Mr. Gates, the Microsoft founder who announced that he would donate $168.7 million to finance research on a malaria vaccine, as part of a new $3 billion World Bank fund to combat the disease.

“While it is true we are not on track to meet the Millennium Development Goals, and it is true that you can say at the present rate of progress in some of the areas it will take 100 years to meet the goals, it is also true that the world is now aware of the challenge,” Mr. Brown said.

Conceived at the United Nations in 2000, the MDGs call for cutting global poverty by half by 2015 and require the wealthy countries to contribute 0.7% of their gross domestic product to causes such as fighting disease, strengthening financial systems, and improving agriculture and education in poorer countries.

“If the world economy is not going very well,” Mr. Gates said, “it’s likely to affect the generosity of rich nations.”

The financial crisis is also likely to have an effect on the economy of poorer countries already suffering from a decline in agriculture production because of the rising costs of fuel and fertilizer.

While Western leaders have blamed Zimbabwe’s descent into poverty in the last decade on the country’s poor — and dictatorial — leadership, Mr. Mugabe yesterday put the onus on the world’s rich countries. It is “crucial that national efforts,” like the one his country is undertaking, “be complemented by appropriate international assistance” from rich nations, he told the General Assembly, demanding that poor nations’ debts be canceled.

Mr. Mugabe, 84, spoke during his first U.N. appearance since he refused to cede power to a rival, Morgan Tsvangirai, who won a national election March 29. As a result, several countries, including America, imposed sanctions on Mugabe allies.

At the General Assembly, Mr. Mugabe called for all sanctions against him to be lifted immediately. The countries that imposed the sanctions “are working on what they call regime change, but I call it Mugabe change,” he later told reporters.