The United States and India have portrayed the completion of a plan to share civilian nuclear fuel and technology as a "historic milestone." Still, much work remains before their nuclear trade can begin.

Officials in both countries appeared relieved at Friday's announcement, which came after months of often frustrating technical talks on a broad deal that was struck two years ago. The deal, however, still must be approved by international regulatory bodies and then face review by a potentially wary U.S. Congress.

Critics say the initiative could spur the spread of nuclear weapons and sends the wrong message to such countries as Iran as they pursue atomic programs. India built its bombs outside the Nuclear Non-Proliferation Treaty, which provides civil nuclear trade only in exchange for pledges from nations not to pursue nuclear weapons. Both the United States and India have nuclear weapons.

The text of the accord was not released, but negotiators said they had settled the knottiest issue: American reluctance to allow India to reprocess spent atomic fuel, a key step in making atomic weapons.

Nicholas Burns, the chief U.S. diplomat at the talks, told reporters the United States agreed to an Indian offer to build a reprocessing facility safeguarded by U.N. inspectors that would prevent fuel from being used to build nuclear bombs.

Indian Foreign Secretary Shiv Shankar Menon, when asked whether the deal would allow India to divert supplies to its weapons program, said: "We are not using it as an excuse to enhance our strategic capabilities. The earlier these countries forget that, the better it is."

Opponents say the extra fuel the measure provides could boost India's nuclear bomb stockpile by freeing up its domestic uranium for weapons. That, they say, could spark a nuclear arms race in Asia.

Democratic Rep. Edward Markey said the Bush administration "has apparently reversed course and decided to allow India to reprocess all U.S.-origin fuel. This is a huge departure from the president's long-standing policy, and Congress is going to want to know how his policies and his actions can possibly match up."

Burns said the deal will "liberate our two countries for a new engagement" after 30 years of tense relations over nuclear matters. It probably also will lead to increased defense cooperation and sales of U.S. military technology, he said.

President Bush praised the deal as "deepening our strategic partnership with India, a vital world leader."

In New Delhi, National Security Adviser M.K. Narayanan said India has "settled for what we think is more than adequate."

The agreement apparently did not deal with another contentious point: India's demand to be allowed to continue to carry out nuclear tests. "If there is a test, we will come to that later on," Narayanan told reporters.

An Indian official, speaking on condition of anonymity because of the sensitive nature of the subject, said India was assured by Washington that if U.S. cooperation ended because of a test, the United States would help find another country to supply fuel to India.

Burns, asked about U.S. assurances to continue India's fuel supply, said it was "hard for me to deal in hypotheticals." But he said that "in the event of any kind of hypothetical disruption of supply," the United States knows "it's important for the Indians to have a continuous supply of fuel."

He also said the United States would ask for all its fuel and technology to be returned should India test a nuclear weapon.

The differing interpretations of what happens in the event India should test a weapon could weaken support for the deal in both countries. In New Delhi, opposition parties on the left and right have expressed misgivings that the pact might undermine the country's sovereignty.

Joseph Cirincione, director for nuclear policy at the Center for American Progress, a liberal think tank, said the deal was "a demonstration of how weak the administration is. They cannot even negotiate a good deal with our friends; they caved on every issue."

For nuclear trade to happen, India must make a separate agreement with the U.N. nuclear watchdog, the International Atomic Energy Agency, and with the Nuclear Suppliers Group, an assembly of nations that export nuclear material.

Burns said both countries hoped that could happen by the end of the year.

The deal allows the United States to ship nuclear fuel and technology to India, which in exchange would open its civilian nuclear reactors to international inspectors. India's military reactors would remain off-limits.

A spokeswoman for the foreign ministry of Pakistan, India's nuclear-armed rival, said that Pakistan was concerned that the deal "would help bolster India's nuclear weapons capability."