PORT-AU-PRINCE, Haiti — The leading edge of a massive relief effort gained a toehold around Haiti's capital yesterday, with the U.S. military taking control of the airport and helicopters ferrying supplies from an aircraft carrier off the coast.

But deep within its neighborhoods, survivors fended for themselves — evacuating those who could go, caring for those who couldn't and putting to rest those who would move no more.

Hundreds of doctors, aid workers, equipment and other assistance beginning to arrive at the airport, where U.S. officials said their goal was to land an aid flight every 20 minutes.

As materials poured in, those responsible for distributing it faced the challenge of finding ways to do so in a city with virtually no infrastructure and a population clamoring for help.

"The biggest crisis obviously is how do you get the resources all over the place?" said David Lipin, of San Carlos, Calif., the commander of the 40-member Disaster Medical Assistance Team sent in from California.

It was one of five such teams that arrived yesterday and deployed by the State Department. About 250 doctors, nurses, emergency medical technicians, surgeons and even a couple of veterinarians were among those waiting to learn where they would be deployed — and how.

Even in good times, Port-au-Prince had a crumbling infrastructure. Now, roads often are barely passable because of rubble strewn across them.

Tom Osbeck, an Indiana missionary whose Protestant-run Jesus in Haiti Ministry operates a school north of Port-au-Prince, told The Associated Press that nerves were becoming increasingly frayed.

"Even distributing food or water is very dangerous. People are desperate and will fight to death for a cup of water," Osbeck said.

As temperatures rose into the high 80s, the sickly smell of the dead lingered over Port-au-Prince, where countless bodies remained unclaimed in the streets. The AP reported that hundreds of bloated corpses were stacked outside the city morgue, and limbs of the dead protruded from crushed schools and homes.

A third of Haiti's 9 million people may be in need of aid. As many as half of the buildings in the capital and other hard-hit areas were damaged or destroyed, according to the United Nations.

There was little evidence of unrest, but also almost no evidence of any official Haitian involvement in the relief effort. Armed police were deployed to at least one gas station to control crowds vying for some precious fuel. Vehicles lined up about a mile to wait for fuel.

Scenes of desperation were everywhere. At one intersection, an elderly woman approached a vehicle, holding out a horribly burned right arm, its skin charred black and the hand swollen. With a bewildered look on her face, she asked where to go for help.

Elie Pierre, a pastor, loaded about 10 members of his family into a small pickup and planned to shuttle them out of the city to a place where they could find better living conditions. He planned to stay behind to find help for his 23-year-old daughter, whose leg was broken during the quake.

Pierre's home was spared, but like many Port-au-Prince residents, his family had been sleeping outdoors for fear of new tremors. A strong aftershock shook the capital about 5 a.m. yesterday.

Pierre shook his head when asked whether he thought help was on the way: He believed no promises right now, he said.

WAITING FOR HELP

Emergency organizations were still waiting for doctors to arrive.

Michelle Chouinard, Haiti director for Doctors Without Borders, said the group hoped to set up medical tents and perform surgeries in coming days. For now, though, its workers could offer only the crudest help: bandages and some floor space or furniture for the seriously injured to lie on.

More than 100 members of the 82nd Airborne Division were in place, and the U.S. military contingent was expected to grow to as many as 10,000 by the weekend. The U.S. deployment includes 4,000 to 5,000 sailors on ships at sea, including the aircraft carrier Carl Vinson, plus 3,000 soldiers and 2,000 Marines on the ground.

President Obama spoke with Haitian President Rene Preval, pledging U.S. support for immediate relief and long-term rebuilding.

Secretary of State Hillary Clinton announced she would visit Haiti today with USAID Director Rajiv Shah to see the relief effort up close. Clinton said she would meet with Preval and other Haitian officials and with U.S. authorities working to get aid to victims.

U.N. Secretary-General Ban Ki-moon said he would also travel soon to Port-au-Prince, and the U.N. said it would launch an appeal for $550 million to provide food, water and shelter to victims.

Ban said the world's response was "generous and robust," but he acknowledged the logistical hurdles. "Although it is inevitably slower and more difficult than any of us would wish, we are mobilizing all resources as fast as we can," he said.

UNKNOWN VICTIMS

There were still no reliable estimates of the number of dead, but some Haitian officials have said the number could exceed 100,000. The Red Cross estimates 45,000 to 50,000 people were killed.

The Reuters news agency quoted Aramick Louis, the secretary of state for public safety, as saying that authorities had buried 40,000 bodies and that 100,000 more people might be dead.

Bodies continued to pile up and Haitians buried them where they could. On the edge of the city's cemetery along a once-grand boulevard, people heaved the dead into a 20-foot mass grave, one of the makeshift burial sites suddenly popping up. It held 60 bodies so far and more were arriving every few minutes by wheelbarrow and pickups festooned with logos like "Love baby."

Sanitation crews went through the streets, loading bodies into dump trucks. In a parking lot outside the city's main morgue, around 2,000 bodies lay in the sun, waiting for someone to identify them and take them away.

'TOUGH, LONG ROAD'

Officials and analysts said the speed with which aid is delivered would be key to preventing people from turning violent in their desperation — at a moment when Haiti's government is almost nowhere to be seen.

Alex Puig, a security expert for International SOS, a Philadelphia-based risk-management company working in Haiti, said some violence was likely, despite the presence of U.S. forces. "It's going to be a tough, long road," he said.

At the airport, foreigners waved their passports to guards as they scrambled to escape the chaos by boarding the departing flights.

"We've had people crying, people passing out," said Muriel Sinai, 38, a nurse from Orlando, Fla.

Some 250 Americans were flown to New Jersey's McGuire Air Force Base on three military planes, The AP reported. U.S. forces in control of the airport initially blocked French and Canadians from boarding planes, even though a French military aircraft stood by. They lifted their cordon after protests from French and Canadian officials.

The State Department said the U.S. death toll was six and predicted it will rise.