“It’s very hard to say,” Nicholas Burns, the chief US negotiator of the deal, told reporters in Washington, when asked how far along would the landmark bilateral pact be when Bush made the trip.

But he said that a complex plan requiring India to separate civilian and military nuclear programs, a key component of the agreement, “might happen before the president’s visit.”

Bush and Indian Prime Minister Manmohan Singh agreed on the basic outline of the civil nuclear cooperation initiative in Washington in July last year and the two countries had hoped to seal an agreement before the president’s visit.

“That remains our plan. And I’ve been in touch with the Indian government this week. I expect to be in touch with them in the coming days, and we hope to reach that goal,” Burns said.

“If we can reach it, then, of course, that will be part of what the president discusses in Delhi. If we cannot, I assume then we’ll keep on working, as diplomats do, to resolve the problem,” he added.

The United States came under fire this week after its envoy in New Delhi warned that the nuclear deal could be scuppered if India voted against Western wishes to refer Iran’s nuclear program to the UN Security Council.

The Indian foreign ministry summoned US ambassador David Mulford and told him that the comments were “inappropriate and not conducive” to US-India relations, India’s foreign ministry said on Thursday.

India has said its decision on how to vote on the Iran nuclear issue within the IAEA would be based on its “own independent judgement.”

Mulford later said his remarks were “taken out of context” and expressed “sincere regrets.”

The bilateral deal would give India access to civilian nuclear technology it has long been denied for conducting nuclear tests and refusing to sign on to the nuclear Non-Proliferation Treaty (NPT).

The accord has been agreed in principle, but still must be approved by the US Congress and the 44-member Nuclear Suppliers Group.

US Secretary of State Condoleezza Rice said on Thursday that the United States and India were making progress, but India had to make some “difficult choices” for the final agreement to be reached but did not give details.

Elaborating on Rice’s statement, Burns said “We, obviously, have to be reassured that that plan is ambitious enough that it will meet the test that the Congress will certainly want to give, in looking at this plan, and also the Nuclear Suppliers Group.”

Some US lawmakers have questioned the wisdom of providing atomic fuel and technology to a nuclear power like India that has refused to sign the nuclear Non-Proliferation Treaty.

They also see India’s response to Iran’s suspected efforts to build nuclear weapons as key to the closure of the deal.

On the basis for his optimism that India could devise a plan to separate itscivilian and military nuclear facilities before Bush’s visit, Burns said: “I’ve been the one negotiating this for six months ... we’re very close to an agreement.”

But he added, “Oftentimes in negotiations, when you get to the end, some of the most difficult issues arise.”

Burns spoke of the need for “further progress” on a few issues which he said were confidential, adding that they “remain barriers to an agreement, but I don’t believe they’re insuperable.”