PORT-AU-PRINCE, Haiti » Doctors and search dogs, troops and rescue teams flew to this devastated land of dazed, dead and dying people yesterday, finding bottlenecks everywhere, beginning at a main airport short on fuel and ramp space and without a control tower.

The international Red Cross estimated 45,000 to 50,000 people were killed in Tuesday's cataclysmic earthquake, based on information from the Haitian Red Cross and government officials. Hard-pressed recovery teams resorted to using bulldozers to transport loads of dead.

Worries mounted, meanwhile, about food and water for the survivors. “;People have been almost fighting for water,”; aid worker Fevil Dubien said as he distributed water from a truck in a northern Port-au-Prince neighborhood.

From Virginia, from France, from China, a handful of rescue teams were able to get down to work, scouring the rubble for survivors. In one “;small miracle,”; searchers pulled a security guard alive from beneath the collapsed concrete floors of the U.N. peacekeeping headquarters, where many others were entombed.

Patience already was wearing thin among the poorest, said David Wimhurst, spokesman for the U.N. peacekeeping mission.

“;They want us to provide them with help, which is, of course, what we want to do,”; he said. But they see U.N. vehicles patrolling the streets to maintain calm, and not delivering aid, and “;they're slowly getting more angry and impatient.”;

In Washington, President Barack Obama announced “;one of the largest relief efforts in our recent history,”; starting with $100 million in aid. The U.S. Southern Command reported the first 100 of a planned 900 paratroopers of the 82nd Airborne Division landed in Haiti from North Carolina yesterday to support disaster relief, to be followed this weekend by more than 2,000 Marines.

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 rescue, medical and other specialists.

But two days after much of this ramshackle city was shattered, the global helping hand was slowed by the poor roads, airport and seaport of a wretchedly poor nation.

Some 60 aid flights had arrived by midday yesterday, but they then had to contend with the choke point of an overloaded Toussaint L'Ouverture International Airport. The Federal Aviation Administration temporarily halted 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 was destroyed in the tremor, complicating air traffic.

Teams that did land then had to navigate Haiti's inadequate roads, sometimes blocked by debris or by quake survivors looking for safe open areas as aftershocks still rumbled through the city. The U.N. World Food Program said the quake-damaged seaport made ship deliveries of aid impossible.

“;Donations are coming in to the airport here, but there is not yet a system to get it in,”; said Kate Conradt, a spokeswoman for the Save the Children aid group. “;It's necessary to create a structure to stock and distribute supplies,”; the Brazilian military said.

The unimaginable scope of the catastrophe left many Haitians, a fervently religious people, in helpless tears and prayer.

Yael Talleyrand, a 16-year-old student in Jacmel, on Haiti's south coast, said thousands of people made homeless by the quake were sleeping on an airfield runway.

One woman, she said, had run through Jacmel's streets screaming, “;God, we know you can kill us! We know you're strongest! You don't need to show us!”;