India's government faces a tight vote of confidence in parliament on Tuesday that will decide the fate of a civilian nuclear cooperation deal with the United States and could trigger a snap election.

The vote pits the Congress-led coalition that negotiated the deal against its former communist allies and opposition parties led by the Hindu-nationalist Bharatiya Janata Party (BJP).

The result is far too close to call, obscured by a flurry of last-minute horse-trading as both sides try to attract the support of smaller, regional or caste-based parties.

Investors are expecting a narrow win for the government, although many remain on the sidelines. Bookmakers also favour the government.

That feeling has helped shares recover after a string of losses, the main share index rising by more than 10 percent in the last three sessions and a further 1.3 percent at 10:50 a.m. (6:20 a.m. British time) on Tuesday.

If the government falls there will probably be an election this year. It is also likely to lead to the scrapping of the civilian nuclear agreement and throw economic policy into limbo just as inflation rises to a 13-year-high.

Likely vote tallies compiled by some of the country's main newspapers and TV channels put the government between two and four votes ahead, but listed several MPs as undecided.

The Times of India said the vote resembled the end of a deadheat 20-over cricket match.

"We are now in the final over, and it still looks like it could be anybody's game," it said.

Prime Minister Manmohan Singh moved the confidence motion with a brief address on Monday, and will make a full defence of the deal and his government's record before the vote.

He smiled and gave a thumbs up and "V" for victory sign for the second day in a row as he entered parliament on Tuesday.

ARRIVING IN AN AMBULANCE

The nuclear deal would grant India access to foreign nuclear fuel and technology, unlocking $40 billion (20 billion pounds) in investment over the next 15 years, according to an Indian business lobby group.

But the communists withdrew their support for the government in protest over the deal, saying it made India a pawn of Washington. The BJP says the nuclear deal limits India's ability to test nuclear weapons.

The vote is so close several MPs who are ill were being flown or wheeled in from hospital, and others, in jail for crimes such as murder and extortion, have been granted temporary release.

As the stormy debate raged on Monday, the mood on the government benches was upbeat, with MPs flashing victory signs and smiling. One opposition lawmaker privately conceded the government could "scrape through by five to six votes".

But weak party discipline and under-the-table deals make the result very far from a foregone conclusion.

A government defeat would be a boost for the BJP, which has won a string of state elections this year against a backdrop of rising inflation and criticism that millions of poor Indians were not benefiting from the booming economy.

It would also boost the standing of Mayawati, leader of an increasingly influential party drawing much of its support from Dalits, formerly known as "untouchables".

Mayawati is trying to project herself as a third force and possible prime minister and has tried to wean away votes from the government.

BJP leader L.K. Advani said his party did not oppose nuclear cooperation or a strategic relationship with the United States, but said the nuclear deal made India "a subservient partner".

A week ago the government was confident of securing a majority with the support of the regional Samajwadi Party (SP), which replaced the communists as its parliamentary support.

Since then there have been signs of a rebellion in the ranks of the SP, making the vote tougher to predict.