US intelligence failed to warn of India's nuclear tests conducted in 1974 and 1998 despite tracking the Asian giant's atomic weapons potential for nearly half a century, according to documents declassified Thursday.
The Indian nuclear activities scrutinised by the US intelligence agents are at the core of a current controversy over President George W. Bush administration's landmark civilian nuclear deal with New Delhi.
The National Security Archive, in releasing 40 secret documents covering the 1958-1998 period, said the Central Intelligence Agency (CIA) and other intelligence groups had been monitoring and analysing Indian civilian and military nuclear energy programs since the 1950s and could have provided decision-makers with "far more detailed assessments."
But the efforts "did not result in US intelligence analysts warning US officials of India's nuclear tests, carried out in May 1974 and May 1998," said the archive, based at George Washington University in Washington.
It keeps declassified US documents obtained through the Freedom of Information Act.
The US intelligence failed because Washington did not devote enough attention to the issue while the Indians kept the nuclear programs a closely guarded secret, said Jeffrey Richelson, the archive's senior fellow.
"So partially it is the failure of the US intelligence community and partially it is the success of the Indian operational security," he told AFP.
Richelson obtained the records while conducting research for his recently published book, "Spying on the Bomb: American Nuclear Intelligence from Nazi Germany to Iran and North Korea."
Based on some documents, he said, India had an aggressive counterintelligence program, including avoiding detection of the nuclear activities by US satellites.
The CIA appointed a panel to investigate the circumstances under which the intelligence gathering strategy failed, and presented a classified report of recommendations, according to the documents.
One CIA secret paper in 1981 mentioned that "China - not Pakistan - is perceived as the major long-term threat to Indian security. "This perception has propelled New Delhi to reject the (Nuclear) Non-Proliferation Treaty and full-scope safeguards in order to retain the nuclear weapons option," it said.
Bush and Indian Prime Minister Manmohan Singh clinched a deal on March 2 that would allow energy-starved India to gain access to long-denied civilian nuclear technology in return for placing a majority of its nuclear reactors under international inspection.
US lawmakers are sceptical about the deal because New Delhi has refused to sign the Nuclear Non-Proliferation Treaty.
The deal can only be effective if Congress amends the US Atomic Energy Act, which prohibits nuclear sales to non-NPT signatories. Critics argue that the agreement smacks of a double standard and could embolden nuclear renegades such as Iran and North Korea even though officials say India's nuclear non-proliferation record has been exemplary.