Dr Singh will meet Bush at 1710 hours local time (0230 hours IST Friday) at the Oval Office in the White House, followed by a working dinner in the Old Family Dining Room.
Indications that the agreement may not be inked on Thursday were given by David Mulford, US Ambassador to India, who received Dr Singh at the Andrews Air Force base near Washington.
"I can't predict when the 123 agreement would be cleared by the Congress," he told media persons but went on to add, "It is not impossible that the deal will get ratified by the end of the current session."
The session, which is scheduled to end on September 26, is expected to be extended by a week.
"So far, the signs have been positive. The very fact that the deal is moving forward in the Congress is a tribute to the US Congress despite its pre-occupation with the trillion-dollar financial bailout package," he said.
The Senate legislation that comes with a rider, which will prevent the transfer of nuclear equipment, materials or technology from the NSG countries or any other source in the event of New Delhi conducting a test, was introduced in the House of Representatives by ranking Republican in the House Foreign Affairs Committee, Florida Congresswoman Ileana Ros-Lehtinen.
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Image: US Ambassador David Mulford receives Prime Minister Manmohan Singh at the Andrews Air Force Base.
Photograph: Paresh Gandhi