By Jonathan Head
South East Asia correspondent, BBC News
For nearly three weeks the Burmese government has insisted that, while it will take relief supplies from overseas, foreign personnel are not welcome.
Than Shwe's offer to let in aid workers appears to be a breakthrough
Hundreds of disaster experts have been left stranded outside the country, waiting for visas, and most of those foreigners already inside have been confined to Rangoon - military checkpoints preventing them from reaching the stricken Irrawaddy Delta.
So the offer by senior General Than Shwe to UN Secretary Ban Ki-moon to allow in "all foreign aid workers, regardless of nationality", appears to be a breakthrough.
If nothing else, it is a significant shift in the official view of the disaster.
Until now the ruling junta had insisted, against all the evidence, that it could look after the more than 2 million victims of Cyclone Nargis by itself, perhaps because of pride, or because of its intense suspicion of any large-scale foreign presence.
Gen Than has had to bow to international pressure, something he rarely does.
But there is an awful lot of detail to be negotiated with the Burmese authorities before we know whether this is a real deal, or just another manoeuvre to deflect international pressure.
The UN has had bitter experience dealing with Than Shwe and his generals in the past; apparent concessions have usually proved illusory.
Help has still to reach many people, three weeks after the cyclone struck
The first point aid agencies want clarified is whether they will get free access to the delta.
They say there is little point in giving visas to all their disaster experts if they are then stuck in Rangoon.
"We already have equipment in Burma which could produce a million litres of drinking water a day," says John Sparrow, from the International Federation of Red Cross and Red Crescent Societies (IFRC).
"Water is critical. But our water and sanitation experts can't get into the delta - so we are training local engineers to use the equipment. But it isn't ideal - they have never done this before."
The IFRC gives a stark illustration of how much needs to be done. It estimates that 1.5 million people are homeless, without any shelter, in the middle of the rainy season.
But the IFRC has only managed to distribute 6,000 temporary housing kits.
To increase that, it needs more foreign experts to find suitable locations, put up the tents, and work out how to run and supply the camps.
"These are people who have been to a hundred disasters, and can make quick judgements about what is needed," says John Sparrow.
"Our local staff are breaking their backs, but they have never seen a disaster on this scale before - they can't cope."
The agencies also want to know that they will be able to run their relief operations themselves, and not through the Burmese army, which is notoriously corrupt and ineffective.
Cyclone survivors have told the BBC that soldiers distribute aid to favoured groups, or often not at all.
One told us that the government's aid effort, praised in the state media as a rousing success, amounted to a choice of one small packet of noodles or one egg per family per day.
There are still large communities who have received nothing.
To meet these enormous needs, the aid agencies would undoubtedly prefer to work independently of the military, but may have to work out some form of co-operation with it.
Then there is the South-East Asian role - the so-called "Coalition of Mercy", whereby the Association of South East Asian Nations, Asean, of which Burma is a member, leads the aid effort.
The idea is that a task force made up of UN experts and two delegates from each of the 10 Asean member states will be formed as the interlocutor between the Burmese government and the aid agencies.
No-one has yet spelled out how this mechanism will work.
One issue does seem clear - the generals are not ready to allow the French, British and US navy ships anchored offshore, with dozens of helicopters on board, to be used to deliver aid.
Aid agencies are trying to find ways to get vital supplies into Burma
They told the UN secretary general that civilian ships and small boats would be acceptable - but one UN official said the idea of foreign navy ships docking was extremely sensitive for them.
Nor will they consider using helicopters available in neighbouring Thailand. That has left the UN scrambling to source heavy-lifting helicopters elsewhere.
They have had to go as far as South Africa - bringing them to Burma will take time and be very expensive. Obtaining boats, trucks and the fuel to run them could also prove difficult.
Three weeks into the worst natural disaster in Burma's recorded history, the relief effort has barely started.
Huge numbers of people are surviving in appalling conditions, with little or no help.
The ruling generals may now realise that they cannot cope.
But for them, security and control have always come first; the lives of their people come second. Those priorities will not have changed.