BANGKOK, Thailand — Cyclone survivors in Burma’s devastated Irrawaddy Delta could require food aid for as long as a year, U.N. officials said yesterday, even as the American military aborted a mission to use helicopters and small boats to deliver aid because Burma’s government ignored repeated offers of assistance.

America had planned to use the helicopters and small boats aboard the USS Essex to deliver much-needed aid to cyclone survivors, but the ruling military junta in Burma rebuffed repeated offers to help with the disaster relief effort, despite the severity of the damage to the region’s rice production.

International aid agencies still are struggling to increase their food delivery capacity in the delta, a complex network of rivers and islands, many of which are only accessible by small boats. Doctors Without Borders (Medicins San Frontiers), the aid agency, said the flow of supplies into the stricken region is still inadequate, and survivors in many remote villages have yet to receive any outside assistance.

However, the Burma junta has refused to permit any foreign military helicopters — either from Western countries or Burma’s southeast Asian neighbors — to join the relief effort.

Admiral Timothy Keating, the top American commander in the Pacific, has ordered the USS Essex to leave the Burmese coast, after what he said were 15 separate efforts to persuade the junta to allow American helicopters to be put to work delivering supplies to survivors.

In a statement yesterday, the White House press secretary, Dana Perino, said the U.S. military assets had been “immediately deployed to Burma in the spirit of goodwill to offer extensive and life-saving assistance to the victims of Cyclone Nargis. Tragically, the Burmese authorities refused to accept this assistance.”

She said that America is committed to aiding the survivors and “to work with ASEAN countries, the United Nations, and non-governmental organizations to do so.” So far, America has provided “more than $26 million in humanitarian aid to the Burmese,” and the U.S. Agency for International Development and the Defense Department “as part of the ongoing airlift, have completed a total of 106 airlifts of emergency relief commodities that will benefit at least 417,000 people,” she said. “The Burmese regime must permit all international aid workers the access necessary to provide the urgently needed assistance. There is no more time to waste.”