India and the United States promised Saturday to sign soon a nuclear cooperation deal which New Delhi said "opened the door for India" to the global nuclear market and tied its future to Washington's.

Indian Foreign Minister Pranab Mukherjee and visiting US Secretary of State Condoleezza Rice told reporters that last-minute hitches had derailed the scheduled signing of the agreement but both looked to the future.

"It is this agreement which has opened the door for India for international nuclear commerce," Mukherjee told a packed press conference with Rice by his side.

"What India and the United States are doing today has direct benefits to our peoples," he added. "India's quest to build a knowledge society leads us to work very closely with the USA."

He added that he hoped the deal "will be signed shortly."

Rice, who had lobbied Congress to approve the deal despite fears it could undercut global efforts to curb the spread of nuclear weapons, had hoped to initial the agreement as the highlight of her brief trip.

However, she told reporters on her plane to New Delhi -- and again at the press conference -- that the signing had to be delayed because of what she described as bureaucratic rather than substantive issues.

"The agreement is done," Rice said. "I don't want anyone to think that we have open issues. These are administrative matters."

The deal has been approved by both houses of the US Congress but has yet to be formally delivered to the White House for President George W. Bush to sign into law.

"The president will sign the agreement very soon," said Rice, adding that both countries would then put their signatures to the deal.

The delay is yet another bump in a three-year rollercoaster for the agreement aimed at lifting a ban on US-Indian civilian nuclear trade imposed after India's first nuclear test in 1974.

But Rice insisted that her visit should still be seen in the wider context of a budding US-India strategic partnership that covers cooperation on defence, education, the economy, agriculture and other fields.

The pact offers India access to sophisticated US technology and cheap atomic energy in return for New Delhi allowing UN inspections of some of its civilian nuclear facilities.

Military nuclear sites will remain closed to international inspections.

Critics say it undermines global efforts to curb the spread of nuclear weapons, because India has refused to sign the international non-proliferation treaty (NPT).

Rice and other US officials had to lobby hard to win approval for the deal from the International Atomic Energy Agency (IAEA), the UN nuclear watchdog, and the Nuclear Suppliers Group (NSG), which controls global atomic trade.

Prime Minister Manmohan Singh, whom Rice was also due to meet, has had a rough ride over the deal at home.

The main opposition Hindu nationalists and the Communists have both slammed it as curbing India's military options and bringing the country's foreign policy too much under US influence.

Rice is also due to meet with opposition leaders.

Even after the accord is signed, US firms cannot do business until New Delhi signs a safeguards agreement with the IAEA.

The US Chamber of Commerce said with India's 34-year nuclear isolation now history, a potential 150 billion dollars of new investments were expected in terms of new nuclear generating capacity by 2030.

The agreement is a key foreign policy success for Bush who agreed to it with Singh in 2005 as part of a strategic partnership between the two biggest democracies.

Rice was scheduled to leave for Kazakhstan on Sunday.