YANGON, Myanmar — U.N. officials today declared the Myanmar delta worst hit by a devastating cyclone a "major disaster," with corpses floating through flooded waters and enormous logistical challenges hampering humanitarian aid efforts.

International aid began trickling into the Southeast Asian country, but much of the Irrawaddy delta, where most of the cyclone's 22,000 victims perished, remains cut off from the world.

"Basically the entire lower delta region is under water," said Richard Horsey, Bangkok-based spokesman for the U.N. Office for the Coordination of Humanitarian Aid. He predicted the casualty figure could rise "dramatically" beyond the latest figure given by Myanmar officials Tuesday.

In Geneva, the United Nations said Myanmar has authorized an airplane to bring U.N. aid supplies to cyclone victims.

But permission was still pending for a U.N. coordination team to accompany the flight, which would take off today. U.N. spokeswoman Elisabeth Byrs said U.N. staff in the Thai capital of Bangkok are also awaiting approval of their visas so they can go to Myanmar and assess damage.

India's meteorological department said today that it had warned Myanmar of the storm two days before it made landfall there, underlining suspicions that the ruling junta did not prepare the country as well as it could have for the disaster.

The state-run Indian Meteorological Department had been keeping a close watch on the depression in the Bay of Bengal since it was first spotted on April 28 and sent regular updates about its progress to all the countries in its path, department spokesman B.P. Yadav said.

Many angry Yangon residents say they were given vague and incorrect information about the approaching storm and no instructions on how to cope when it struck. Most of the information was broadcast on television, of little use to much of the population in a country where power and TV access is spotty.

On Monday, first lady Laura Bush criticized the government for not adequately warning its citizens about the storm.

Aid workers were able to start distributing essential relief supplies in the region today, including water purification tablets, mosquito nets, plastic sheeting and basic medical supplies. But heavily flooded areas are accessible only by boat, Horsey said.

"Teams are talking about bodies floating around in the water. ... It's a huge, huge problem just to get these goods out," he said.With as many as 1 million left homeless after Cyclone Nargis hit over the weekend, the international community was struggling to deliver aid in the military-ruled country, which normally seeks to shut out foreign officials and restricts their access inside the country.

State television on today quoted Yangon official Gen. Tha Aye as reassuring people that the situation was "returning to normal" in certain areas that were hit by the cyclone.

President Bush on Tuesday called on Myanmar's military junta to allow the U.S. Navy to help search for the dead and missing. But Myanmar's military, which regularly accuses the United States of trying to subvert the regime, was unlikely to accept U.S. military presence in its territory.