NEW DELHI - INDIA'S parliament on Tuesday was to hold a make-or-break confidence vote that could bring down the government, lead to early elections and end a controversial nuclear energy deal with the US.

After weeks of intensive horse-trading and hours of stormy debate pitting the Congress-led government of Prime Minister Manmohan Singh against left-wingers and Hindu nationalists, the outcome was still uncertain.

Projections by Indian news channels and papers showed the government was headed into the test just a whisker ahead - with a projected advantage of a mere one or two votes.

'It is a tight race, no doubt about that,' analyst and opinion pollster Yashwant Deshmukh said.

Still, he said the government could just pull through: 'The government would never have gone for the vote if they were not sure of winning.' The prime minister has exuded confidence, and Tuesday's debate is expected to see Congress bring out its elegant and charismatic leader, Italian-born widow Sonia Gandhi, in a final bid to win over undecided lawmakers.

The vote was triggered after a bloc of left-wing and communist parties pulled their support for Dr Singh in protest over the deal with Washington designed to bring India into the global loop of nuclear commerce after decades of isolation.

The deal allows India, which has nuclear weapons and refuses to sign the nuclear Non-Proliferation Treaty, to be treated as a special case on condition it separates its civil and military programmes and allows some UN inspections.

Government officials gave an impassioned defence of the deal during Monday's parliamentary debate, arguing that the country's 1.1 billion people badly need alternative sources of energy to avert an impending fuel crunch.

'The question is do we want to come out of nuclear isolation? I want India to become an economic power, a superpower,' Finance Minister P. Chidambaram told the 543-seat Lok Sabha, or lower house, as debate resumed on Tuesday.

India's power stations cannot keep up with demand, coal is running out, and power cuts are frequent - not the recipe for continued strong growth of more than nine percent, officials argue.

But left-wingers and the main opposition Hindu nationalist Bharatiya Janata Party (BJP) say the deal ties traditionally neutral India too closely with the United States, and would compromise the country's nuclear weapons programme.

They are equally confident they can win and bring down the government.

Indian media said the coalition would go into the vote with just a tiny advantage.

The Times of India newspaper said 269 lawmakers would support the government, while 267 were against and four undecided.

The Hindustan Times said 270 deputies would back the government, and 266 were against. The NDTV news channel said the government had 272 likely votes of support, and the opposition 268. The Hindu newspaper put both camps at 267 votes each, with the remainder undecided.

The race is so tight that the government has let MPs serving jail terms out of prison to vote. The opposition has also paid for special planes to bring in lawmakers who were in hospital.

The communists have also been trying to widen the terms of the debate - speaking out against rising food and fuel prices, and arguing that hundreds of millions of poor have been left behind in India's economic boom.

Voting is expected to take place late on Tuesday following a second day of speeches in the house, including presentations by Gandhi and her son and heir apparent, Rahul.