PORT-AU-PRINCE, Haiti — Emergency aid flowed from around the world toward Haiti yesterday, only to confront a reality that grew more desperate by the hour: Crippled ports and communications left stunned earthquake survivors on their own to scavenge for food and water, carry away legions of dead and dig frantically for voices calling out from under the rubble.

President Obama promised $100 million and the full resources of the U.S. government for what he said would be one of the largest relief efforts in recent history. U.S. officials said 30 countries had either sent aid or promised to do so. Rescue teams from eight countries already were on the ground.

Two days after a magnitude 7.0 earthquake devastated Port-au-Prince, there was little evidence of the aid effort in the capital of the hemisphere's poorest country.

"In Haiti, you're lucky if they come with a screwdriver," said Jean Marc Mercier, a Haitian American who spent the past two days hunting for survivors in the wreckage of the Hotel Montana, a longtime gathering spot for diplomats, journalists, humanitarian workers and businessmen.

The toppled six-story hotel was an exception to the scenes of abandonment elsewhere; a rescue team newly arrived from Virginia was combing the debris.

Mercier, who runs a computer business in Haiti, said he and others had been burrowing by hand with others toward voices calling out from deep inside the wreckage. They had managed to save one woman, an aid worker.

"Last night after I went to bed, all I heard were the voices in my head. One guy told me not to bother: 'Go help people who are in better shape. There is no way you are getting to me,' " said Mercier, 44. "I wasn't able to sleep all night."

Aid officials said the risk of violence and looting would increase as scant food and water run out and frustrated families fail to find medical care for the injured.

The international Red Cross estimated 45,000 to 50,000 people were killed in Tuesday's cataclysmic quake, based on information from the Haitian Red Cross and government officials, according to an Associated Press report.

All over Port-au-Prince, it seemed, the living bore the dead — in the beds of pickups, in wheelbarrows, on makeshift stretchers. At a hospital named Saint Marie, crowded a day earlier by dozens of people seeking help, the courtyard was empty except for two cleaners mopping bloody water into the street.

AID BOTTLENECK

Both the air and seaports were proving to be bottlenecks for the international aid effort.

Dr. Paul Farmer, a Harvard medical professor and U.N. deputy special envoy to Haiti, said the quake-damaged seaport is "basically shut down."

Some 60 aid flights had arrived by midday yesterday but they then had to contend with the chokepoint of an overloaded Toussaint L'Ouverture International Airport, the AP reported. At midday, the Federal Aviation Administration said it was temporarily halting all civilian flights from the U.S. at Haiti's request, because the airport was jammed and jet fuel was limited for return flights. The control tower had been destroyed in Tuesday's temblor, complicating air traffic. Civilian relief flights were later allowed to resume.

"There's only so much concrete" for parking planes, U.S. Air Force Col. Buck Elton said at the airport. "It's a constant puzzle of trying to move aircraft in and out."

UNICEF, the U.N.'s children's charity, was amassing supplies in Panama for an airlift. The agency sent one plane with medical kits, blankets and tents to Port-au-Prince yesterday, but the plane could not land and had to return to Panama.

"It's really a logistics nightmare," Farmer said. "We need to fix the port and open up other land bridges and air spaces where planes and helicopters can land."

OBAMA SEEKS HELP

In Washington, Obama enlisted both of his immediate predecessors, Presidents Bill Clinton and George W. Bush, to lead the initiative, following an example set by Bush after the 2004 Southeast Asian tsunami. It was his first presidential request of Bush, whom he criticized for his handling of the aftermath of Hurricane Katrina.

"You will not be forsaken; you will not be forgotten," Obama said, addressing the people of Haiti. "In this, your hour of greatest need, America stands with you."

U.S. officials were able to evacuate between 300 and 400 U.S. citizens by air, most of them to the neighboring Dominican Republic, which shares the island of Hispaniola with Haiti.

One immediate focus of the U.S. effort was restoring communications, which were so bad that Obama was unable to reach Haitian President Rene Preval yesterday afternoon.

A U.S. diplomat was among the dead. State Department spokesman P.J. Crowley said Victoria DeLong, 57, a cultural affairs officer, had been stationed in Haiti since last year. He said she was from California, but her hometown was not immediately available.

From Europe, Asia and the Americas, other governments, the U.N. and private aid groups were sending planeloads of high-energy biscuits and other food, tons of water, tents, blankets, water-purification gear, heavy equipment for removing debris, helicopters and other transport, and teams of hundreds of search-and-rescue, medical and other specialists.

TOPPLED BUILDINGS

In the downtown area, many old French columns and porticos toppled into the wide and once-splendid Grand Rue. The Casernes Dessalines, the infamous Army barracks where enemies of the Duvalier dictatorship were tortured and killed, still stood. But many government buildings, including the tax office, were complete losses.

Chaotic lines formed at gas stations, though it was unclear if any gasoline would be pumped. Those with enough fuel created a noisy traffic jam on one main boulevard heading out of the capital.

People scavenged for water, carrying empty canisters in the street.

One elderly man, who wanted to be identified by his first name only, Milton, said Haitians were hoping that U.S. Marines, who have been deployed in the past during times of political upheaval, would come again.

"When the U.S. occupation is good and big, it creates work, builds roads, helps people," he said. Not only that, Milton insisted that Marines tended to toss uneaten food into the city's omnipresent mountains of garbage.

"They bring good ham and cheese," he said, "And you know it's good food because they have eaten it."