WASHINGTON  Former Presidents George W. Bush and Bill Clinton began a new venture on Saturday to raise money for the Haitian relief effort from corporations, foundations and ordinary Americans, as President Obama pledged to ramp up the American response to the devastating earthquake.

The three men, who have collectively occupied the White House for the past 17 years, stood side by side in the Rose Garden to announce the effort. “We just met in the Oval Office  an office they both know well,” Mr. Obama said.

Describing the phone calls he made to the two men in the aftermath of the earthquake, he said: “They each asked the same simple question: ‘How can I help?’ ”

Image American soldiers controlled the entrance to the airport in Port-au-Prince. By Monday, 9,000 to 10,000 troops are expected to arrive to help with the relief effort. Credit... Orlando Barria/European Pressphoto Agency

As the death toll in Haiti grows, Mr. Obama said, the American response, both private and public, must grow with it.