Indian Foreign Secretary Shyam Saran and U.S. Undersecretary of State Nicholas Burns are leading the negotiations.
Washington has offered to provide India with civilian nuclear technology, but wants to ensure New Delhi does not use the equipment for military purposes.
Burns said Thursday that differences remain between the two sides, and he is not sure an agreement will be ready by next week.
President Bush said Wednesday he wants to come home from India with a deal on the nuclear issue so he can start promoting it to Congress, which must give its approval.
Some U.S. lawmakers oppose transferring nuclear technology to India, arguing that would undermine the Nuclear Non-Proliferation treaty, which India has not signed.Some information for this report was provided by AFP, AP and Reuters