Under the agreement, first hammered out during the Indian prime minister's visit to the White House in July last year, the US will facilitate the transfer of nuclear technologies to India by lifting sanctions that were imposed when India first carried out nuclear tests in 1974 and again in 1998.
It will also facilitate the free flow of uranium for India's civilian nuclear-power programme.
In exchange, India, which has not signed the nuclear non-proliferation treaty (NPT), will have to separate its estimated 22 military and civilian nuclear installations by 2014 and allow monitoring by the International Atomic Energy Agency (IAEA).
The deal is expected to boost India's nuclear energy supply from the present 3% to 25% by 2050.
Manmohan Singh told the Indian parliament in February he hoped for "new opportunities and possibilities for promoting (India's) energy security and pathways to accelerated social and economic development".
But many of India's nuclear scientists are apprehensive about the conditions stipulated in the deal and fear losing control of their nuclear programme.
"There are contradictions in the prime minister's statement (in parliament) and I have doubts about the basic assumptions and premises on which the deal is based," a leading Indian nuclear scientist AN Prasad told Aljazeera.net.
Prasad, former chief of the flagship nuclear science institute, Bhaba Atomic Research Centre (BARC), believes the deal has made India "dependant" and "vulnerable", not strong and secure as claimed by the prime minister.
Singh has had to give long justifications about the deal in and outside parliament, not only to allay the concerns of the scientific community but also to silence his allies from leftist parties who comprise a 100-strong parliamentary bloc.
Leftist and Muslim groups loudly
opposed Bush's visit in February
The left bloc believes that the deal was a quid pro quo for India's vote against Iran at the IAEA, which helped refer the Islamic Republic's nuclear programme to the UN Security Council.
Leftist MPs say the deal also marks a fundamental shift in India's position - from being a non-aligned country to becoming America's ally.
"Under Bush's leadership, America is dictating to India its foreign and economic policies ... which amount to an outrageous interference in our internal affairs," Communist Party of India leader D Raja told Aljazeera.net before Bush's visit.
Officials involved in the trade negotiations, however, dismiss the opposition.
"The left is pursuing its old policy of opposing any agreement with the US. It never supported India's nuclear programme but is now overanxious to protect it from IAEA inspections," Naresh Chandra, India's former ambassador to the US, said.
The left's demands to ratify the deal in parliament have also been rejected by the government, and they now hope the US Congress would shoot it down.
"The left is pursuing its old policy of opposing any agreement with the US. It never supported India's nuclear programme but is now overanxious to protect it from IAEA inspections"
former Indian diplomat
Non-proliferation pundits in the US have long maintained that the Bush-Singh agreement violates US laws that prohibit nuclear business with countries that have not signed the NPT.
They also fear that by helping India expand its weapons production, the US could inadvertently reignite an arms race in the region, especially with nuclear neighbour Pakistan.
The chances of the deal falling through in the US Congress are "fairly high", says Lloyd Rudolph, Harvard professor and US foreign policy analyst.
Rudolph told Aljazeera.net that Bush signed the deal based on politics rather than principles.
Sign of weakness
"Bush is in a weak and declining position politically. He could not afford another failure and go back home without an accord," Rudolph said.
But officials in the Bush administration believe the deal would eventually convince India to sign the NPT.
"It is a net gain for non-proliferation and it will eventually bring India into the NPT regime," Nicholas Burns, US under-secretary of state, said after the bill to amend US law and ratify the deal was introduced in Congress in mid-March.
Bush said the deal will help India
cut down on use of fossil fuel
And this is what worries Indian scientists.
"It is an obsession with them (the US) to cap our nuclear programme by bringing it under some sort of control," said Prasad as he emphasised that America just "cannot stomach the idea of anyone else progressing".
Prasad is equally apprehensive about international inspections. "Safeguards are not as easy as it looks. I have worked at the IAEA and know how intrusive it is. How are we going to stop the inspectors and where will we draw the line when there is no watertight compartmentalisation of the civilian and military programme?"
India has a unique, three-stage, inter-linked nuclear-power generation programme in which pressurised heavy water reactors (PHWRs), fuelled by natural uranium, generate weapon-grade plutonium.
In stage two, fast-breeder reactors (FBRs) use the plutonium-based fuel to breed Uranium-233 before advanced heavy water reactors or AHWRs in stage three burn U-233 with thorium to generate power.
FBRs, developed by India on its own, are not only the crucial link between the first and the last stage of the programme but are also specific to India's energy security in view of the huge reserves of thorium, estimated at 290,000 tonnes, which could yield 530,000 megawatts of electricity, enough to last 300 years.
"Under Bush's leadership, America is dictating to India its foreign and economic policies ... which amount to an outrageous interference in our internal affairs"
Thanks to the pressure of scientists, FBRs were kept out of the deal - and therefore, international monitoring - but they are still worried about the deal's fallout on the programme.
It is unlikely the deal and its ramifications will be resolved for another few months.
In addition to a vote pending in the US Congress, the transfer of nuclear technology to India will also be put to a vote at a meeting of the Nuclear Suppliers Group in Vienna, Austria.
The Group, comprising the world's major nuclear powers, was established in 1975 to monitor and rule on the transfer of nuclear technologies to nations which could pose a threat to the international community.
The Nuclear Suppliers Group is expected to rule on the Indo-US deal in June.