A key US lawmaker threatened Wednesday to hold up a landmark US-India nuclear agreement unless nuclear supplier states adopt a provision terminating the deal if India conducted a nuclear test explosion.

Howard Berman, chairman of the House of Representatives foreign affairs committee, said if the 45-nation Nuclear Suppliers Group (NSG) did not impose such a condition, the deal could not be approved before President George W. Bush leaves office in January 2009.

"Given the lateness in the Congressional session, it would be better to review these complex matters in the next Congress when they can receive a full and serious examination," the Democratic legislator said in a letter Wednesday, to Secretary of State - Condoleezza Rice.

The US House and Senate will

adjourn in late September ahead of the presidential and congressional elections two months later.

Bush and Indian Prime Minister Manmohan Singh agreed to the nuclear deal in 2005, under which the United States will provide energy-starved India civilian nuclear fuel and technology.

The United States and other key developed states suspended nuclear trade with India after New Delhi fired its first nuclear weapons test in 1974, and the new deal was part of a strategic partnership between the world's two biggest democracies.

The Indian parliament endorsed the deal last month after a tense debate following which the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog agency, approved key safeguards for the agreement to be implemented.

The Bush administration later this month apparently intends to seek an

exemption for India on nuclear commerce guidelines from the NSG with "few or none of the conditions" contained in a special US law governing the deal, Berman said.

A key condition under the law --the Henry J. Hyde United States-India Peaceful Atomic Energy Cooperation Act of 2006 -- "is the immediate termination of all nuclear commerce by NSG member states if India detonates a nuclear explosive device," he said.

Any exemption of this provision for India "would be inconsistent with US law, place American firms at a severe competitive disadvantage, and undermine critical US nonproliferation objectives," he said.,

"It would also jeopardize congressional support for nuclear cooperation with India, this year and in the future," he warned.

Daryl Kimball, .executive director of the US Arms Control Association, said Berman's letter was "very useful and significant.