This came in the address of Indian Prime Minister Manmohan Singh to a joint meeting of Congress on Tuesday, an honour bestowed only on the closest of US allies.
The address came one day after President George Bush said he will push for a reversal of US policy so Washington can help India's nuclear power programme.
Any such change in policy would require Congress' support.
Lawmakers applauded his comments on nuclear cooperation.
"The field of civil nuclear energy is a vital area for cooperation between our two countries," Singh said, describing India's track record on nuclear nonproliferation as "impeccable".
He said India has "adhered scrupulously to every rule and canon" even though "we have witnessed unchecked nuclear proliferation in our own neighbourhood which has directly affected our security interests", an apparent reference to Pakistan, its neighbour and longtime rival.
"We have never been, and will never be, a source of proliferation of sensitive technologies."
It was the eighth time in the past five years that a foreign visitor has addressed a joint meeting of the House of Representatives and the Senate.
Manmohan Singh (L) outlined
common areas of interest
Singh told lawmakers that the objective of his three-day Washington trip was "to lay the basis for transformed ties between our two great countries".
Relations between the world's oldest and largest democracies have often been shadowed by suspicion but have improved in recent years.
Singh, standing before Vice-President Dick Cheney and House Speaker Dennis Hastert, said the two countries have common interests in such areas as the fight against terrorism, joint work to combat Aids and dual efforts to promote democracy - as well as cooperation in developing new energy resources.
He noted one area where the two countries do not agree: US resistance to India gaining a permanent seat on the UN Security Council.
"The voice of the world's largest democracy surely cannot be left unheard on the Security Council when the United Nations is being restructured," Singh said.
On economic themes, he assured lawmakers that "India's growth and prosperity is in America's own interest," and said India needs massive foreign direct investment.
"I hope American companies will participate in the opportunities we are creating," he said.
Singh's speech was the first by an Indian leader since former Prime Minister Atal Bihari Vajpayee in 2000.