The US House of Representatives has approved an agreement to share civilian nuclear technology with India.
Energy-hungry India needs nuclear power
The legislation must now be approved by the US Senate before being signed into law by President George W Bush.
The deal offers US nuclear technology to energy-hungry India in exchange for access to Indian civilian reactors.
Critics say the deal will hurt efforts to control nuclear arms, as the Indian government refuses to sign the nuclear Non-Proliferation Treaty.
A spokesman for the Indian foreign ministry welcomed the vote in the House of Representatives.
He said that it "demonstrates the broad political consensus in the US for the promotion of Indo-US relations in all fields".
"We must nevertheless await the finalised text of the legislation which will emerge after a Senate vote," the spokesman said.
He said there was still concern in India - which had been conveyed to the US - to ensure that the final legislation does not deviate from earlier agreements between the two countries.
Mr Singh (left) and President Bush see the deal as crucial
Before the agreement can become law, US legislators must vote to exempt India from a ban on nuclear trade with countries which do not agree to full international inspections of their atomic facilities.
Democratic Congressman Tom Lantos said the deal would be a "tidal shift in relations between India and the United States".
He said he believed the United States and India Nuclear Co-operation Promotion Act would lead to "a new era of mutual respect and co-operation".
The bill was passed by a vote of 359-68.
The proposed agreement reverses US policy to restrict nuclear co-operation with Delhi because it has not signed the nuclear Non-Proliferation Treaty (NPT), and has twice tested nuclear weapons, in 1974 and 1998.
Mr Bush finalised the agreement during a landmark trip to India in March.
Under the deal, India's nuclear weapons sites will remain off-limits.
Critics of the deal say it could boost India's nuclear arsenal and sends the wrong message to countries like Iran, whose nuclear ambitions Washington opposes.
"By shipping India fuel for its civilian reactors, this legislation potentially frees up their [India's] entire supply of domestic uranium for use in weapons," House Democrat Ed Markey said before the vote.
NUCLEAR POWER IN INDIA
India has 14 reactors in commercial operation and nine under construction
Nuclear power supplies about 3% of India's electricity
By 2050, nuclear power is expected to provide 25% of the country's electricity
India has limited coal and uranium reserves
Its huge thorium reserves - about 25% of the world's total - are expected to fuel its nuclear power programme long-term
Source: Uranium Information Centre
India's nuclear-armed neighbour Pakistan has asked the US to address what it calls its legitimate needs in the civilian use of nuclear power.
Correspondents say there are fears the deal may spark off an arms race in South Asia with recent unconfirmed reports that Pakistan is a building new nuclear reactor to produce weapons-grade plutonium.
India's main opposition Bharatiya Janata Party has called the deal "unacceptable".
It said that it would make India "perpetually dependent" on the US for all initiatives in the application of nuclear energy.
India's Communists, who are allies of the ruling Congress-party led federal government, have also expressed their reservations about the deal.
India has made clear that the final agreement must not bind it to supporting the US's Iran policy and does not prevent it from developing its own fissile material.