The Indian leader was speaking at an event to dedicate to the nation's service two new nuclear power reactors in western India.
Energy security was critical to sustaining the long-term economic growth of India, Asia's third largest economy, and the country could not pick between different fuel sources, he said.
"India is now too important a country to remain outside the international mainstream in this critical area.
"We need to pave the way for India to benefit from nuclear commerce without restrictions."
The text of a civilian nuclear energy co-operation deal with Washington was finalised last month but has faced strong opposition from communists who, although outside of Singh's coalition, shore it up with their support.
The deal aims to lift a three-decade ban on sales of US nuclear fuel and reactors to India, imposed after it conducted a nuclear test in 1974 while staying out of non-proliferation agreements.
While the deal has been hailed by Washington and Delhi, the communists say it compromises India's sovereignty and and forces it to accept US influence over foreign and strategic policies.
India needs to conclude a safeguards agreement with the International Atomic Energy Agency, get unanimous backing of the Nuclear Suppliers Group and the approval of the US Congress before the deal can come into effect.