The new goal was a $5 billion increase for an initiative that marks a shift in the global fight against hunger.
The leaders meeting in Italy said they wanted to focus less on sending food to the poor and more on helping small farmers in developing countries produce more and better crops.
Premier Silvio Berlusconi, the host of the meeting of the Group of Eight and other nations, said that leaders decided to raise the initial goal from $15 billion during talks held with African leaders in the morning. Washington was expected to commit $3 billion, and Paris $2 billion, delegates said, but it was not immediately clear if there were solid commitments for the remaining amount.
The United Nations welcomed the new strategy as an overdue shift away from a focus on delivering emergency food aid. Anti-poverty groups, however, said the funding was insufficient, and they have criticized developed countries for failing to make good on past pledges.
The G-8 talks were expanded to include emerging economies and, on Friday, African nations.
The initiative calls for helping the private agricultural sector and small farmers, particularly around harvest time, and puts emphasis on aid to families and women. It says that any improvement in agricultural production should be coupled with measures to help countries to adjust to changing conditions caused by global warming.
"We will aim at substantially increasing aid to agriculture and food security," the 27 nations said. They said the money would be dedicated to a "coordinated, comprehensive strategy focused on sustainable agriculture development, while keeping a strong commitment to ensure adequate emergency food aid assistance,"
Angola said it greatly appreciated the new commitments, saying they represented "very significant steps."
"Rebuilding the infrastructure and constructing new infrastructure in Africa will create wealth that will contribute to reducing poverty that unfortunately still exists in the country," said the southern African nation's ambassador to Italy, Manuel Pedro Pacavira.
In a separate statement, leaders said it was important to increase access to water and sanitation and the G-8 promised to assist African countries in doing so.
Food security, or ensuring adequate access to food, has jumped to the fore of the political agenda recently. High prices last year led to food riots in some countries.
While food aid will still be necessary to prevent people from starving, the new approach puts emphasis on a longer-term aim.
Increasing small farmers' productivity would have long-term impact on world hunger, regional trade and eventually help curb immigration toward Europe and other rich nations, delegates and experts said.
"It's a total shift, a welcome and encouraging one," said Jacques Diouf, the chief of the U.N. Food and Agriculture Organization.
"You solve the problem of hunger by giving the necessary tools to farmers who are in these poor countries so they can produce food," Diouf told the AP.