By Andrew Harding
Asia correspondent, BBC News
It was an astute and unexpected gamble.
The referendum announcement took many by surprise
Last Saturday, Burmese state radio abruptly declared that it was "a suitable time to change from a military government to a democratic civilian administration".
This dramatic announcement came out of the blue - a reminder that Burma is ruled by the whims of an isolated general who once decided to move the country's capital virtually overnight on the advice of his astrologers.
In fact, Senior General Than Shwe has been talking about his "roadmap" towards "disciplined democracy" for so long that many had assumed it was simply another delaying tactic by a junta which has clung ruthlessly to power for decades.
But on Saturday, a reasonably precise timetable was suddenly produced.
A referendum, the radio announcer declared, would be held in May on a new constitution. Democratic multi-party elections would follow smoothly two years later.
We shall probably never know exactly what prompted Than Shwe to make this brusque move. Perhaps he had been planning it all along.
Many weary Burmese may choose to vote for a flawed document in the hope that it will at least be an improvement on the status quo
More likely he was prodded by China, and saw it as a useful way to undercut international pressure on his government.
He may also have been motivated by concerns about his own failing health and the security of his family in a notoriously unforgiving political system.
Either way, the result is that Burma is now moving towards what may well prove to be a defining political moment.
The stakes are very high.
Will the junta manage to control the process, sideline the UN, outsmart its western critics and emerge in full control of a sham democracy?
Or will opposition forces finally find a way - either by fighting or joining the roadmap process - to push Burma towards genuine democratic reform?
Right now, the odds seem to be stacked in the junta's favour.
Let us start with the new constitution.
The drafting process could have been an opportunity (even at this late stage) to bring Burma's feuding political factions together.
Instead the document was drawn up by a handpicked assembly, without the participation of the country's main democratic opposition and its leader Aung San Suu Kyi.
It was finalised in secrecy, and has yet to be revealed in full.
It is not clear what role - if any - Aung San Suu Kyi will play
However it is already clear that the constitution will ensure the military retains a stranglehold on power in Burma, with a large share of seats in government and parliament, and the right to sweep aside civilian rule whenever required.
The constitution is also almost certain to bar Aung San Suu Kyi from power (because she was married to a foreigner) and it may well find an excuse to do the same for her party, the National League for Democracy (NLD).
Of course the constitution could be rejected in May's referendum. But that seems unlikely - criticism of the constitution is a criminal offence.
The authorities are bound to keep a tight control over any voting process - a secret ballot may not be deemed necessary - and will have an army of well-rewarded, and often thuggish, loyalists from the mass organisation, the Union Solidarity and Development Association, to "encourage" participation.
After years of political stagnation, many weary Burmese may choose to vote for a flawed document in the hope that it will at least be an improvement on the status quo.
And what of Aung San Suu Kyi? Still under house arrest, she faces a difficult choice.
Should she endorse the broad aims of the roadmap and use her considerable moral authority try to find a way to nudge the process in a more democratic direction?
Or should she and the NLD boycott it, and hope that their supporters can frustrate the military as they did when the NLD won the, quickly overruled, election of 1990?
Both options carry substantial risks, and after experiencing years of repression, the NLD is not the force it once was.
Climate of fear
There is, of course, the strong possibility of more street protests.
Those who led the demonstrations last August and September are without doubt preparing more of the same.
Burma's leaders have showed that they will crush any dissent
The Alliance of All Burmese Buddhist Monks and the 88 Generation Students have described the roadmap as a "declaration of war" and May's referendum as "a battlefield".
That could spell real trouble for the junta. The economy remains in dire straits and the hardships which prompted last year's protests are now even more acute.
In that sense, time is not on the generals' side. They need to move promptly to fix a new political system before popular anger boils over.
But the military authorities showed in September that they are ready to crush all opposition - even if that means violently confronting the country's revered monks.
Given the pervasive atmosphere of fear in Burma, it seems unlikely, though of course not impossible, that tens of thousands of civilians will once again dare to take to the streets.
It is hard to judge the real impact of international pressure on such an insular regime. But for what it is worth, China and the South East Asian regional grouping Asean will probably be keen to give the roadmap the benefit of the doubt, at least in the short term.
The UN has been effectively sidelined - its envoy, Ibrahim Gambari, is being kept out of the country, presumably until the new constitution is already a fait accompli.
Western countries will no doubt continue to call for a more inclusive, democratic reform process, and perhaps tighten their financial sanctions against the junta.
But as one Western diplomat privately admitted, "It's going to be tough... Than Shwe has muddied the waters... It's a clever plan," which leaves the West with few options but to "work with the grain" of the roadmap.