Asia Focus

Left-wingers, who triggered the vote by withdrawing their support, say the deal ties traditionally non-aligned India too closely with the United States. The government needs a simple majority of votes, but opposition parties - including the left and the Hindu nationalist Bharatiya Janata Party (BJP) - are equally confident they can push the world's largest democracy into early polls.

If the government loses the vote, elections must be held within six months.  Experts say they would likely take place once the monsoon season ends in late September. The race is so tight, and the stakes so high, that the government has let six MPs serving jail terms out to vote. Meanwhile, the opposition has reportedly paid for charter flights to bring in ailing lawmakers, including one who has had heart bypass surgery.

Here is a look at the possible scenarios, according to India's political experts

Government wins

·         The Congress party-led ruling United Progressive Alliance (UPA) wins the vote of confidence.

The government continues in power, moves ahead with a civilian nuclear deal with the United States and continues with pending economic reforms. It also gets time to get organized before a general election in May 2009.

The government loses

·         The ruling UPA coalition loses the vote of confidence and the government falls.

The president could ask the prime minister to continue in power as a caretaker government.

The Election Commission of India will then fix a date and an early election will be called, most likely by the end of the year.

or

The opposition could try to form an interim government before the scheduled May 2009 election. This is an unlikely scenario because the main Hindu nationalist opposition Bharatiya Janata Party (BJP) has said it would prefer elections if the government falls.

A tie

·         The vote of no-confidence ends in a tie and the speaker in parliament casts his vote to decide the outcome. In this case, the government could fall as the speaker, Somnath Chatterjee, a member of the Communist Party of India (Marxist), would probably vote against the government.

Nuclear deal is core issue

The core issue is the nuclear deal, which spans India's energy security as well as its place in the world. India, which tested nuclear weapons in 1974 and 1998 and refuses to sign the nuclear Non-Proliferation Treaty, is currently barred from buying nuclear technology and fuel. The deal would allow such purchases but subject India's civilian nuclear sites to international controls - aimed at ensuring that any purchases are not diverted for military uses.

Opponents say the deal would compromise India's position as a beacon of neutrality, and that the requisite UN inspections would limit India's ability to develop its weapons program and deter its main regional rival Pakistan. They also argue that there are strings attached and that doing a deal with Washington would undermine its freedom to buy oil and gas from countries like Iran, or shop for armaments with traditional suppliers like Russia.