* U.N., EU hail breakthrough three weeks after storm struck

* Junta agrees to allow aid workers of all nationalities

* Deal includes hardest-hit Irrawaddy Delta

* U.S. and French navy ships still await Myanmar permission (Adds EU, U.S., French comment paras 7-16)

By Patrick Worsnip

NAYPYIDAW, Myanmar, May 23 (Reuters) - Myanmar's junta agreed on Friday to admit foreign aid workers of all nationalities to the delta area worst hit by Cyclone Nargis, in what the U.N. called a breakthrough for aiding survivors.

Western disaster experts, largely kept out of the Irrawaddy Delta and restricted to the former capital Yangon, welcomed the news but wanted more details on the deal struck by U.N. Secretary-General Ban Ki-moon and junta supremo Than Shwe.

"The general said he saw no reason why that should not happen ... as long as they were genuine humanitarian workers and it was clear what they were going to be doing," a U.N. official with Ban said.

Asked whether the agreement on relief experts was a breakthrough, Ban replied: "Yes, I think so. He has agreed to allow all aid workers regardless of nationalities."

The U.N. chief said he hoped the agreement "can produce results quickly. Implementation is the key."

Disaster experts say that unless the generals open their doors, thousands more people in the Irrawaddy Delta could die of hunger and disease, adding to the nearly 134,000 reported killed or missing in Cyclone Nargis, which struck three weeks ago.

European Union humanitarian commissioner Louis Michel expressed relief at the news.

"It is now clear that our joint diplomatic efforts have delivered concrete results," he said in a statement.

"We have no more time to lose, so it's imperative that the Myanmar authorities immediately provide the international community with the practical details of the agreement. The real work of providing life-saving assistance starts now."

'NO' TO FRENCH AND U.S. SHIPS

The reclusive junta has accepted relief flights into Yangon from many countries, including the United States, its fiercest critic. But it has rejected offers of French and American naval vessels delivering aid.

U.N. officials said the ships were "a very sensitive idea for them -- any suggestion they should dock".

French President Nicolas Sarkozy condemned the refusal to let the navy ship Mistral enter Myanmar territorial waters.

"I profoundly regret this decision. Once again the junta has made the wrong choice," Sarkozy said during a visit to Angola. He said France was still studying ways to deliver the aid, possibly by helicopter or via the nearest Thai port.

The United States said it would not keep its navy ships waiting indefinitely for the generals' permission.

"We're going to continue to try to encourage them...We're still hopeful," Pentagon spokesman Bryan Whitman said.

"But at some point -- we're talking, you know, days, maybe weeks, not months -- if the position of the Burmese government doesn't change, then eventually we will have to make a decision to reallocate those Naval assets."

"PRETTY SHARP"

On a mission to help 2.4 million left destitute by the cyclone, U.N. chief Ban and his aides met Senior General Than Shwe for more than two hours in the remote new capital of Naypyidaw, 250 miles (390 km) north of Yangon.

Ban was accompanied by reporters from international media, a rare concession from the junta, which is under tougher Western sanctions for cracking down on pro-democracy protests last year.

For the meeting with the top U.N. diplomat, 75-year-old Than Shwe wore his habitual dark green shirt, open at the neck, laden with medals and decorations befitting a man who has spent 55 years in the former Burma's all-powerful army.

"We got the impression that the man in control is pretty sharp," one U.N. official said.

When his aides suggested that maybe too many concessions were being made, Than Shwe butted in: "I don't see a problem."

Than Shwe said Myanmar was open to receiving relief supplies and equipment from civil ships and small boats. Ban said he had also agreed to allow the airport in Yangon to be used as a logistical hub for distribution of aid, which is still only trickling in.

World Vision, one of the few charities operating in Yangon, said any concessions from the junta were welcome, however small.

"Any positive noises are better than nothing," spokesman James East said in the Thai capital, Bangkok. "We are cautiously optimistic. The critical thing is access to the delta."

Ban saw the extent of the disaster for himself on Thursday, flying in a helicopter over flooded rice fields and destroyed homes in the delta, the former "rice bowl of Asia" that bore the brunt of the storm and its 12 foot (3.5 metre) sea surge.

Ban will attend a joint U.N. and Association of Southeast Asian Nations (ASEAN) donor-pledging conference in Yangon on Sunday. However, ASEAN Secretary-General Surin Pitsuwan said countries would be reluctant to commit money until they are allowed in to assess the damage for themselves. (Additional reporting by Emmanuel Jarry, Andrew Gray in Washington, Ed Cropley in Bangkok; Writing by Grant McCool and Mark Trevelyan)

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