Weak party discipline, backroom deals and possible accidents like MPs falling ill or mistakenly spoiling a ballot mean the vote on Tuesday is almost impossible to predict, analysts and political strategists say.

All of which is making Prime Minister Manmohan Singh's four-year-old government increasingly nervous.

It contrasts with a week ago when the government believed it had secured a majority with support of the Samajwadi Party to replace the exit of Left allies in protest against the nuclear pact.

"It will be a nail-biting finish," said political analyst Mahesh Rangarajan.

The vote in the 543-member Parliament will see the result determined by a handful of MPs from small, regional-based parties. Many are still keeping their intentions close to their chests, waiting to wiggle out concessions from either side.

Numbers are in flux. But the government is roughly a dozen votes short of the 272 majority.

There are around 20 MPs who are undecided, torn between supporting the opposition led by BJP and the Leftists on the one hand, and the Congress party-led coalition on the other.

"As of now, Congress does not have the assured support of the majority and therefore I would reduce its prospects further to around 50 pc," analyst Seema Desai of Eurasia consultancy wrote in an e-mail message.

"Right up till the vote, things could change" said Desai, who last week had given the government's survival chance at 70 per cent.

The government was more confident last week with the momentum of gaining SP backing. Some analysts believe it may still win.

"I still think the government will weather the storm, just," said Kuldip Nayar, a political expert and history author who predicted a majority of 8-10 votes. "But Congress leaders are not happy dealing with such tight margins."

DESPERATE MEASURES

But in a sign of how close the vote could be, the government has been taking some desperate measures.

It has renamed Lucknow airport to honour the father of RLD’s Ajit Singh.

"Last week it was taken for granted that the government would win," said Arun Jaitley, senior BJP leader. "Now that's not so. I think government support is slipping."

What has changed is that the government has failed to secure the open support of smaller parties. There are also reports of rebellions within the ranks of allies such as the SP.

Other MPs wonder whether it is worth voting for a government that is increasingly unpopular amid signs of rising inflation hitting millions of poor consumers.

General elections must be held by next May at the latest in any case.

"Many parties are thinking about their future in the next general election, not the trust vote. Many think Congress will lose anyway, so why vote for them now?" Jaitley said,

In 1999, a BJP-led Govt fell after losing a confidence vote by a margin of just one, after one MP fell ill and another abstained, Rangarajan said.

Since then politics has become even more unpredictable, analysts say, with small, regional parties holding greater sway and MPs more ready to defect for cash or influence.