RAMSTEIN AIR BASE, Germany : US Secretary of State Condoleezza Rice flew Friday to India to showcase an historic civilian nuclear deal but raised doubts about whether it would be signed on her trip.

A signing delay would be another hitch in a three-year rollercoaster for an agreement aimed at lifting a ban on US-Indian civilian nuclear trade imposed after India first set off a nuclear test explosion in 1974.

Rice put it down to a bureaucratic rather than a substantive issue.

"There are a lot of administrative details that have to be worked out," Rice told reporters on her plane before it landed for refuelling at the Ramstein Air Base in Germany.

"I'll let you know (if the signing is on) but the whole purpose of this trip is to move forward, not to look at where we are," she said on the flight from Washington to New Delhi.

She put the deal in the context of a budding US-India strategic partnership that covers cooperation on defence, education, the economy, agriculture and other fields.

The United States now has a "broad, strong and deep" relationship with India, which is a growing economic power, she said.

The green light for her trip -- and an apparent signing ceremony -- came days after US lawmakers voted for the agreement based on accompanying safeguards to curb the spread of nuclear weapons technology.

Under Secretary of State for Arms Control and International Security John Rood told AFP on Thursday that Rice would sign the agreement -- that would allow US firms to sell reactors to India -- on her weekend trip to New Delhi.

She was due to meet Prime Minister Manmohan Singh, Foreign Minister Pranab Mukherjee, and other Indian officials.

Rice did not elaborate on the administrative snags, but said she did not have to wait for President George W. Bush to sign the deal before she could ink it herself. Bush has said he looks forward to signing it.

Daryl Kimball, executive director of the US Arms Control Association and a strong critic of the pact, said the "Indians are not going to be happy" with a promise Rice made to Congress in return for the deal's quick adoption.

Rice pledged to push as hard as she can to have the Nuclear Suppliers Group "amend its guidelines to prohibit the transfer of enrichment and reprocessing technology to states that haven't signed the NPT," Kimball said.

India, which has never signed the Non-Proliferation Treaty (NPT), badly wants such technology which can be used for both peaceful and military purposes, Kimball said.

Singh has had a rough ride over the deal in his own country.

The Hindu nationalist Bharatiya Janata Party (BJP) and the communists slammed it as curbing India's military options and bringing the country's foreign policy too much under US influence.

Even after the accord is signed, US firms cannot do business until Delhi signs a safeguards agreement with the International Atomic Energy Agency (IAEA) and the Convention on Supplementary Compensation for Nuclear Damage.

India last month wrote a letter of intent to sign up to the convention, which Kimball says US businesses want in order to reduce their liability in the event of a catastrophe.

The US Chamber of Commerce said with India's 34-year nuclear isolation now history, a potential 150 billion dollars (107 billion euros) 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 signed it with Singh in 2005 as part of a strategic partnership between the two biggest democracies.

He prevailed in the face of critics inside and outside Congress who warn that the pact will undermine the standards that the United States helped develop over decades to check the spread of nuclear weapons know-how.

During her talks in India, Rice said she would discuss India's support for boosting Afghan political and economic institutions.

"Obiously we have information sharing (about Islamist militants) as well but I would emphasis the political and economic support for Afghanistan," Rice said.

After her trip to India, she was due to visit Afghanistan.

- AFP /ls