None of the leaders of the G8 group of industrialised nations are attending the conference, apart from Silvio Berlusconi, the Italian prime minister, at the meeting of delegates from 60 nations.
Humanitarian agencies had hoped the summit would agree greater assistance to the world's one billion hungry people.
Frederic Mousseau, an Oxfam spokesman, said: "Rich countries are failing to show enough interest and urgency.
"At the G8 in Italy this summer they pledged $20bn for agriculture over three years, so they believe they have done enough. They haven't - and the $20bn is a mirage."
Pope Benedict XVI will be an introductory speaker at the "Hunger Summit", which is being held at the Food and Agriculture Organisation (FAO) headquarters.
Luiz Inacio Lula da Silva, the Brazilian President, Muammar Gaddafi, Libya's leader, Egypt's Hosni Mubarak, Hugo Chavez of Venezuela, and Robert Mugabe, Zimbabwe's president, are also slated to attend.
Avvenire, an Italian bishops' newspaper, complained that the draft final declaration failed to mention the $44bn Jacques Diouf, the FAO head, has requested for agriculture in less developed nations.
"Every six seconds a child dies of hunger," Diouf said last week.
"This enormous tragedy is not only a moral outrage and an economic absurdity, but also it presents a serious threat to our collective peace and security."
The draft declaration seeks to commit leaders to a new strategy to promote agricultural development aid, but lacks a target date for eradication of hunger - set by the UN at 2025.
The draft was "just a rehash of old platitudes," Francisco Sarmento, Action Aid's food rights co-ordinator, said.
The Islamic Development Bank committed $1bn for projects with the FAO on Sunday, the agency said.