A leading Democratic lawmaker has released a secret Bush administration letter that says the U.S. has the right to immediately stop nuclear trade with India should that country conduct an atomic test.

Rep. Howard Berman is making public the State Department's Jan. 16 answers to key congressional questions at a sensitive moment in the countries' pursuit of a deal that would reverse three decades of U.S. policy by shipping atomic fuel to India in return for international inspections on India's civilian reactors.

Members of the Nuclear Suppliers Group of countries that export nuclear material are gathering in Vienna on Thursday and Friday to discuss the deal. The Bush administration must get an exemption for India from the NSG's rules before the U.S. Congress could ratify the proposal, which would allow the sale of nuclear materials to a country that has tested nuclear weapons but has refused to sign nonproliferation treaties.

The U.S. view on India's potential testing is important because India, looking to ease strong domestic opposition, has said that there is nothing in the agreement with the U.S. that would place a ban on future Indian nuclear tests or affect Indian decision-making in foreign policy.

In the letter addressed to Berman's predecessor as chairman of the House of Representatives Foreign Affairs Committee, the late Tom Lantos, the State Department said that stopping nuclear trade with India would be "a serious step" and would come only under circumstances that include the detonation of a nuclear weapon.

U.S. assurances to India to continue to supply fuel, the letter said, "are intended to guard against disruptions of fuel supply to India that might occur through no fault of India's own," such as a trade war and market disruptions.

"The fuel supply assurances are not, however, meant to insulate India against the consequences of a nuclear explosive test or a violation of nonproliferation commitments," the letter said.

In response to an unusual request by the Bush administration, senior U.S. lawmakers had kept secret the State Department's answers to more than 40 questions about an agreement that settled technical matters on a broad nuclear cooperation deal that was struck in 2005. The administration's request had come as the nuclear deal faced strong political opposition in India that jeopardized the government. U.S. critics said keeping the answers to the congressional questions secret was meant to stop publicity that could have killed an already wounded accord.

Some countries at the Nuclear Suppliers Group have offered strong opposition to an exemption for India. The Vienna talks this week are expected to focus on amendments to a U.S.-proposed draft statement that would allow India access to other nations' nuclear fuel and technology.

Time, however, is running out for U.S. lawmakers to consider the deal. Congress has only a few weeks of work in September before it is scheduled to break for the rest of the year to campaign for November elections that will determine the next president and the political future of many current lawmakers.

Supporters of the civilian nuclear deal say atomic cooperation with India would provide crucial energy to a democratic, economically vibrant country. Critics say it would ruin global efforts to stop the spread of atomic weapons and boost India's nuclear arsenal.