The arrival of more American forces comes amid widespread violence and looting.
However, UN and US officials have downplayed the threat of violence.
Aid workers are starting to expand their efforts to earthquake-affected areas outside the capital, including Leogane, Gressier, Petit-Goave and the coastal town of Jacmel.
'Test of resolve'
The US Air Force C-17 dropped the relief supplies on Monday into a secured area five miles (8km) north-east of Port-au-Prince, US Army spokeswoman Maj Tanya Bradsher was quoted as saying by the Associated Press.
Haitians flock under a US helicopter delivering aid supplies in Port-au-Prince
She said the aircraft had flown out of Pope Air Force Base in North Carolina.
Last week, US Defence Secretary Robert Gates said airdrops had been ruled out because they might do more harm than good.
Mr Gates warned that they could trigger riots if there was no proper structure on the ground to distribute supplies.
AT THE SCENE
Adam Mynott, BBC News, Haiti
The director of the main port in Haiti says the bulk of the aid should be arriving by sea but the earthquake devastated the harbour.
It is an extraordinary sight - large sections of the main wharf have toppled into the sea. The whole length of the wharf is littered with 40ft steel containers leaning at angles.
The access road is rent with 6in gaps and the main crane has toppled forward, leaning at a drunken angle, half submerged in the water.
The director says it may take months, but they will get the port open again. However, it has become another symbol of an aid operation that has failed to deliver supplies quickly or to where they are needed.
The BBC's Nick Davies in Port-au-Prince says that with the delays in getting aid out from the airport, the US military are now securing the areas before the pallets of food and water are parachuted in.
Meanwhile, thousands of extra UN police and peacekeepers are due to be deployed as a way of increasing security to stop the looting from spreading, our correspondent says.
The Security Council is expected to vote later on a recommendation by Secretary General Ban Ki-moon to boost UN troop numbers in Haiti by 2,000 for six months, and UN police numbers by 1,500.
British Prime Minister Gordon Brown said on Tuesday that Haiti remained a major test for the international community.
"It is a test of our compassion. It is a test of our resolve. And it is also a test of our ability to co-ordinate our actions together."
France's co-operation minister, Alain Joyandet, had suggested on Monday that the US was "occupying" Haiti and urged the UN to "clarify" the US role.
However, a statement from President Nicolas Sarkozy on Tuesday said France was "very satisfied" with the co-operation and praised the US for its "exceptional mobilisation".
As well as problems at the airport, there were also major problems at Port-au-Prince's main seaport, which was badly damaged by last week's earthquake.
The port's director told the BBC it could be months before it is fully operational, although one large shallow-draught US barge has been unloaded.
On Tuesday, UN spokeswoman Elisabeth Byrs said 90 people had been pulled out alive since the earthquake and rescue efforts were now concentrated outside of the capital.
AID PLEDGES TO HAITI
EU - $604m (420m euros; £371m)
US - $100m pledged in immediate aid, with promise of more later
She insisted there was still hope for survivors. "The climate is mild, there are significant air pockets. The problem is dehydration but for the moment there is still a chance," she said.
At least 70,000 people who died in the earthquake have already been buried.
On Tuesday, the Paris Club of creditor governments, including the US, UK, France and Germany, called on other nations to follow its lead in cancelling debts to Haiti. Venezuela and Taiwan are the biggest other creditors.
Meanwhile, the bodies of eight Chinese nationals killed in the quake have arrived back in Beijing in a high-profile ceremony attended by relatives and top officials.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.