"By the end of this day I am confident we will truly have helped Haiti along the road to a new and better future," Ban said.
Haiti's President Rene Preval asked donors to focus on education and help its 9 million people provide for their own future.
"Let us dream of a new Haiti whose fate lies in a new project for a society without exclusion, which has overcome hunger, in which all have access to secure shelter ... (and their) health needs provided," he told diplomats and ministers from more than 130 countries.
Clinton announced the United States' pledge of $1.15 billion over the next two years. Catherine Ashton, the European Union foreign affairs chief, then announced the EU's pledge of 1.235 billion euros, equivalent to over $1.6 billion.
The $3.8 billion Haiti is seeking for the next 18 months is just the initial part of a $11.5 billion package Preval's administration wants to rebuild schools, hospitals, courthouses and neighborhoods destroyed in when the magnitude-7 earthquake pulverized its capital on Jan. 12.
Haiti's government has detailed its plans for the money in a 55-page rebuilding plan that lays out the interim reconstruction committee. It includes requests for $350 million in direct budget support to the government, which Edmond Mulet, the top resident U.N. envoy there, said is crucial for the country's progress.
"We need Haiti to succeed," Clinton said. "What happens there has repercussions far beyond its borders."
She said the donors conference was not only to pledge financial support but "to offer support in a smarter way."
Haiti's leaders must guide "a transparent recovery," Clinton stressed, and the international community must change its past practice of working around the government and ensure that it is working with the government.
At the core of the quake-ravaged country's request for help is the Interim Haiti Recovery Commission, or IHRC, which will be co-chaired by Bill Clinton and Haitian Prime Minister Jean-Max Bellerive.
The commission's two-dozen members will be tasked with coordinating and paying out the aid money expected to flow in. It is a key step to allaying donor concerns over Haiti's history of official corruption and political unrest who want assurances that the money will go where it is intended.
Its members include some Haitian legislators, local authorities, union and business representatives, and a delegate from the 14-nation Caribbean Community trade bloc. The board will also have a representative of each donor who is pledging at least $100 million over two years or $200 million of debt reduction -- currently the United States, Canada, Brazil, France, Venezuela and European Union along with the Inter-American Development Bank, World Bank and United Nations.
The former U.S. president was tapped for the role earlier this week, Bellerive said. Clinton, who as U.N. special envoy to Haiti visited three times since the earthquake, will likely be spending much more time in the impoverished country in his new role.
Cheryl Mills, the chief of staff to Hillary Clinton, said the aim is to have Haiti take over control of the reconstruction commission after 18 months.
The board Clinton will help lead is a source of consternation among some Haitian lawmakers, who are now considering a legislative package submitted by Preval to approve the commission's authority. Opposition lawmakers are threatening to block the bill unless Preval's administration first publishes a report on how aid money was spent in the initial aftermath of the disaster.
However, passage is possible without them, as the president's newly formed Unity Party has the largest voting bloc in both houses.
The earthquake struck just miles (kilometers) from Haiti's capital on Jan. 12 and destroyed its government and commercial center, home to nearly a third of the population. Varying government estimates -- which have risen without explanation in the lead-up to the conference -- put the death toll between 217,000 and 300,000 people.
An estimated 1.3 million people lost their homes in a country that before the quake was the poorest in the Western hemisphere.
Hundreds of thousands are living on cracked streets and perilous hillsides under flimsy tarps, at risk for disease, floods and landslides with rains starting to pick up. There have been increasing reports of violence, including rape and sexual assault, in the camps which have little lighting and scant security at night.
Human rights advocates are demanding transparency, accountability and coordination that have been absent in the past. Several petitioned the Organization of American States on March 23 with arguments that $2.2 billion in immediate post-disaster aid had not helped most victims.
A group of protesters gathered across the street from the U.N. headquarters, waving Haiti's blue-and-red flag and denouncing a process they said has not included most of the Haitian people.