New Delhi:  Once seen as a shoe-in for the ruling coalition, a parliamentary vote of confidence that will determine the fate of India's government and a civilian nuclear deal with the United States is going down to the wire.

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 regional Samajwadi Party (SP) to replace the exit of communist 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 lawmakers 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.

Assured support

There are around 20 lawmakers who are undecided, torn between supporting the opposition led by the nationalist Bharatiya Janata Party and the communists 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 per cent," analyst Seema Desai of Eurasia consultancy wrote in an email 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 a regional airport to honour the father of one wavering MP and secured the release from prison of five other lawmakers to vote. Four of them were in jail for murder. Rahul Gandhi, heir to the Nehru-Gandhi dynasty and potential Congress leader-in-waiting, even hinted the government may fall. "If the government falls in the process, so be it," he was quoted as saying in The Times of India.

The realities of having to secure a majority in parliament that represents more than 1 billion people of different castes, tribal and political groups appear more complicated than ever.

"Last week it was taken for granted that the government would win," said Arun Jaitley, chief election strategist for the BJP. "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.