Speaking to reporters aboard her plane, which stopped at Ramstein to refuel, Rice said Friday it was not certain whether she would sign the agreement during her one-day visit to New Delhi because "there are a lot of administrative details left to be worked out."

Legislation authorizing the controversial deal won final congressional approval on Wednesday. Rice said U.S. President George W. Bush looks forward to signing the bill, but that is not a precondition for her discussions in India.

The agreement on civil nuclear cooperation allows American businesses to begin selling nuclear fuel, technology and reactors to India in exchange for safeguards and U.N. inspections at India's civilian - but not military - nuclear plants.

Critics in India argue the constraints compromise their country's right to conduct nuclear bomb tests.

Whether a signing ceremony is held or not, "I'm going to draw a line under this" deal "one way or another because it's time to put the historic agreement - to say that that's done and move on to what else we can do" to strengthen and broaden the relationship, she added. The Bush administration considers the deal a crowning achievement of the president's second term in office.

It could, however, turn out to be the last major diplomatic achievement of a presidency that is struggling in its final months on a number of other fronts, including a setback in relations with Russia after its invasion of Georgia and the prospect of a breakdown in a nuclear agreement with North Korea.

Rice said she spoke Friday morning with the administration's chief nuclear envoy to North Korea, Christopher Hill, who was in Pyongyang this week to try to persuade the North Koreans to resume dismantling their nuclear problem in exchange for energy aid. She said she and Hill did not discuss what progress he may have made; they intend to meet Monday in Washington.

In the onboard interview, Rice stressed that she saw the importance of her visit to New Delhi as focusing on the future, rather than celebrating the completion of the civil nuclear agreement.

"This is a relationship that has now a firm foundation to reach its full potential," she said. "It removes for India a barrier to full integration on a whole range of technologies," and it opens the way for closer U.S.-India cooperation in other areas such as defense, agriculture and education. India built its nuclear bombs outside the Nuclear Non-Proliferation Treaty, which it refuses to sign. It has faced a nuclear trade ban since its first atomic test in 1974; its most recent nuclear test blast was in 1998.

Throughout the Cold War, relations between India and the United States were chilly. In the past decade, however, ties have grown closer in a range of areas, including trade, energy and security. The United States is now India's largest trading partner.

U.S. opponents of the nuclear agreement say lawmakers rushed consideration of a complicated deal that could spark a nuclear arms race in Asia. The extra fuel the measure allows India to purchase, those critics say, could boost India's nuclear bomb stockpile by freeing up its domestic fuel for weapons.

Increasingly, India figures into U.S. strategic interests in other ways, including its long standoff with neighboring Pakistan. The Pakistani government has focused so much on what it perceives as an Indian threat that it has limited its security efforts against militants along its border with Afghanistan.