The two leaders met on the sidelines of the G8 summit in the Russian city of St Petersburg.
The controversial deal would give India access to US nuclear technology.
It reverses US policy which had restricted nuclear co-operation since India tested a nuclear weapon in 1974.
The agreement was finalised during US President George W Bush's visit to India in March.
The accord has been hailed as historic by some, but critics say it will damage non-proliferation efforts.
A US Senate committee and a House of Representatives panel backed the deal last month.
Reports said Mr Singh sought Mr Bush's support for successful completion of the deal during the 40-minute meeting.
"There are some concerns which worry us and worry our parliament," Mr Singh was quoted telling Mr Bush during the meeting by the Press Trust of India.
"We are a democracy and we are accountable to the parliament which zealously keeps a watch on what we do and what we do not," the report quoted him saying.
Mr Bush was quoted telling Mr Singh that he was "optimistic" about the deal being passed.
"It's an important piece of legislation. I'm optimistic we'll get that passed," the Associated Press quoted him telling the Indian prime minister before the meeting.
The final vote on the proposed agreement is not expected till the middle of July.
The proposed agreement reverses US policy to restrict nuclear co-operation with Delhi because it has not signed the nuclear Non-Proliferation Treaty (NPT), and has twice tested nuclear weapons in 1974 and 1998.
Tags
News India Dalits Hindhus Congress Education Caste system Untouchables China
