YANGON, Myanmar — The U.N. secretary-general flew to Myanmar today to steer a 50-nation conference that will pledge funds for survivors of Cyclone Nargis after the country's military junta promised to open its doors to critically needed foreign help.

Three weeks after the cyclone struck, frustrated foreign aid workers were ratcheting up preparations to finally go into the Irrawaddy delta with food, drinking water, medicine and other relief.

U.N. Secretary-General Ban Ki-moon, who had wrested the open-door agreement from the ruling generals, was flying early today to Yangon from Bangkok, Thailand, to attend the conference of some 50 countries along with U.N. and non-governmental aid agencies.

After weeks of stubbornly refusing assistance, Myanmar's ruling generals have told the United Nations they are now willing to allow workers of all nationalities to help survivors of the storm that left about 78,000 people dead and another 56,000 missing.

The ability to assess the situation will be critical in securing pledges from foreign governments, and the junta's about-face was seen as a concession to get more aid when the potential donor nations meet in Yangon, Myanmar's biggest city.

An estimate released Saturday by the U.N. said that while about 42 percent of the 2.4 million people affected by the storm had received some kind of emergency assistance, only 23 percent of the 2 million people living in the hardest-hit areas had been reached.

U.N. Secretary-General Ban Ki-moon said Myanmar's ruling generals had told him that international aid workers will be able "to freely reach the needy people," a pledge the junta has not publicly acknowledged.

Ban, who has made visits to Thailand and China, flew into Myannar for the conference on this morning.

On Saturday, Ban and the Thai prime minister inaugurated a new hub for relief efforts, a warehouse at Bangkok's old international airport. Ban said authorities were planning two flights a day from there into Yangon, using Ilyushin 76 and Antonov 12 airplanes.

The World Food Program — which has gotten the go-ahead for helicopter operations — and other non-governmental aid organizations also will use the hub.

On the first flight from the hub, UNICEF sent three mobile water treatment plants that can produce 10,000 liters of water a day to help 3,200 people. "It will save lives," Ban said.

The United Nations has launched an emergency appeal for $201 million. That figure will likely increase once disaster relief experts are able to survey the stricken Irrawaddy delta.

So far, the U.N. has received about $50 million in contributions and about $42.5 million in pledges in response to the appeal, said Stephanie Bunker, spokeswoman for the U.N. Office for the Coordination of Humanitarian Affairs.

Myanmar has estimated the economic damage at about $11 billion.

The conference Sunday is being sponsored by the U.N. and the 10-country Association of Southeast Asian Nations, which is taking the lead in organizing the delivery of aid to Myanmar, one of its members.

ASEAN Secretary-General Surin Pitsuwan, calling it a "Coalition of Mercy," said he believed donors would show their goodwill, but added that they would be unlikely to honor pledges if the junta failed to follow through on its promises for international access.

"I don't think we have any doubt that there will be a lot of goodwill coming through," Surin said. "But again it will depend on how we carry out this goodwill, or administer this goodwill, with the cooperation of Myanmarese authorities."

"We expect no obstacles," he said.

The junta's apparent concession came Friday after three weeks of blocking relief for cyclone survivors.

"I want to be optimistic, but I'm skeptical," Lionel Rosenblatt, president emeritus of U.S.-based Refugees International said. "The devil is going to be in the implementation."

The possible breakthrough distracted attention from the junta's widely criticized decision to push ahead Saturday with a constitutional referendum in Yangon and hard-hit areas of the delta.

Turnout for the vote appeared low, which was expected since many potential voters remained consumed with rebuilding their lives and the government already had announced the final results.

The rest of the country voted May 10 on the controversial proposed charter and state radio has reported that the delayed balloting could not reverse the constitution's reported approval by 92.4 percent of the 22 million eligible voters.

Myint Maung, a lawyer who voted against the constitution along with five family members, said officials at his polling station in Yangon's Sanchaung township told him that under half of the 2,000 eligible voters turned out Saturday.

A cyclone victim, 27-year-old Naing Lin, said he was "not even aware of the referendum, and even if I were, I wouldn't be interested."

Naing Lin, whose entire immediate family died in the storm, was staying at a monastery in Kyonemaw village southwest of Yangon.

The government has been widely criticized over the proposed charter, not only for the timing of the vote so soon after the cyclone, but because it is viewed as an effort to strengthen the military's grip on power.

The xenophobic junta has kept the delta virtually off-limits to foreign aid workers, who have been barred from traveling outside Yangon.

Aid agencies said much needs to be clarified from Ban's meeting, ranging from logistical issues about when aid workers' visas will be granted to how long they will be allowed to stay in Myanmar and where they can work.

Senior Gen. Than Shwe has refused to relent on the landing of military ships — U.S., French and British warships are waiting with aid off Myanmar's coast but have not been allowed to dock. Myanmar's junta is nervous about any shore landings because it fears an invasion or political interference.