World donors sought to bolster Afghanistan's fragile leadership Thursday with pledges of more than $21 billion in aid as the need to help secure and feed the country overshadowed concerns about pervasive corruption.

The United States led the way, promising $10.2 billion.

Donors pledged to coordinate their aid better than in the past, when billions poured into the country, often with little oversight. In a final statement, they also urged Afghan officials to tackle corruption.

French Foreign Minister Bernard Kouchner, in announcing the final sum, said the figure was beyond his dreams. It exceeds the $15 billion to $20 billion Afghan officials had hoped for.

"Afghanistan has reached a decisive moment for its future. We must not turn our back on this opportunity," first lady Laura Bush said.

The new pledges are in addition to $25 billion pledged by the international community since 2002. However, only $15 billion — 60 percent — of those previous pledges has been honored so far.

That's because it is almost impossible to police how and where the aid is spent.

Security questions loom over every aid project since Karzai's Western-backed administration has only a shaky grip on much of the country. The heroin trade is a key part of the economy, as is corruption.

Most Afghans lack proper sanitation and 80 percent have no electricity at home, despite $15 billion in international aid since the Taliban's ouster in 2001. Life expectancy remains under 50 years, and food shortages over the past year have pushed many Afghans to the brink.

The Taliban still recruit in desperately poor rural areas, and their insurgency continues to claim lives more than six years after U.S.-led troops invaded following the Sept. 11 terrorist attacks blamed on al-Qaida, whose militants the Taliban were sheltering.

Afghanistan's still-tenuous security climate was highlighted by tensions over U.S. airstrikes that may have killed friendly fighters in Pakistan along the Afghan border. The bombings Tuesday fueled anti-U.S. sentiment in Pakistan, and could set back efforts to stem violence in the lawless region.

Meanwhile, Defense Secretary Robert Gates was expected to push NATO allies meeting Thursday in Brussels to send more troops and police instructors to Afghanistan. NATO's mission in Afghanistan has more than doubled, to 51,000, over the past two years, but commanders say it still lacks units for critical tasks like air transport and intelligence.

Karzai promised to fight the graft that bleeds aid dollars and that the World Bank says is crippling the legitimacy of his government.

"Afghanistan needs large amounts of aid, but precisely how aid is spent is just as important," Karzai told the conference.

Donors agreed that the needs are urgent and enormous, and won't be solved immediately.

"The vast majority of the work is still to be done. It will be difficult, it will take time," Australian Foreign Minister Stephen Smith said.

Karzai said giving farmers alternatives to growing opium poppies and trafficking drugs is crucial to Afghanistan's future.

"Opium is about survival" for these farmers, he said.

Noting the "major transformation" Afghanistan has gone through since 2001, he presented a development plan to the donors that says his country needs $50 billion over the next five years to boost an economy shattered by a quarter-century of war.

U.N. representative Kai Eide, looking at Afghanistan's progress in recent years, said: "It is a very fragile success and it must be consolidated."

Secretary of State Condoleezza Rice said the U.S. is dedicating $10.2 billion over two years for Afghan development. The money is a mix of what Congress already has approved for this year and next, and what the Bush administration is still seeking before it leaves office.

Other major donors included the Asian Development Bank, $1.3 billion; the World Bank, $1.1 billion; Britain, $1.2 billion, and the European Union, $775 million.

A similar donors' conference in 2006 garnered pledges of $10.5 billion.

The United States is the single largest donor to Afghanistan, not counting the cost of the ongoing war against insurgents. That war is unlikely to end soon: The Afghan government, in its development strategy unveiled Thursday, envisions peace by 2020.