When Manmohan Singh, India's prime minister, last visited Washington, in 2005, he was presented with a historic gift by then President George W. Bush: the US-India civilian nuclear agreement that ended New Delhi's decades-old “nuclear pariah” status and was seen as being implicitly aimed at containing a rising China.

Barack Obama has already struck a warm personal rapport with Mr Singh on the sidelines of two G20 summits this year. But as Mr Singh begins a state visit to Washington today, there is concern in New Delhi that India has moved down the US's list of priorities, anxieties re- inforced by Mr Obama's emollient overtures to China during his eight-day east-Asian tour last week.

“I don't think the US has made up its mind as to where it sees India in its geopolitical view,” said Arundhati Ghose, India's former ambassador to the United Nations.

But US officials have been at pains to emphasise the long-term importance to Washington of its relationship with India, the world's largest democracy.

“Few relationships matter more to our collective future, or hold greater promise for constructive action on the challenges that matter most for us, than the partnership between the US and India,” William Burns, US undersecretary of state for political affairs, said.

But C. Raja Mohan, an influential Indian strategic affairs analyst, said relations between New Delhi and Washington had suffered from “a bit of exhaustion from both sides” after the breakthroughs of the past few years, which saw the burial of decades-old cold war-era suspicions.

“The Obama administration is very keen on this relationship and wants to move it forward, but in terms of operationally, what's happened because of the financial crisis, there is that much attention to China,” he said.

Mr Singh's trip to Washington is seen as the opportunity to revive and reinvigorate those ties.

Certainly working relations have never been better. In the wake of last year's Mumbai attacks, in which 166 people died, including six Americans, India and the US have engaged in unprecedented intelligence co-operation.

India also signed a $2.1bn (€1.4bn, £1.3bn) deal this year to buy eight maritime reconnaissance aircraft from Boeing, its largest-ever acquisition of US military hardware, and American companies are vying for a $10bn deal to supply 126 fighter jets to update India's Soviet-era strike force. Bilateral trade, meanwhile, has doubled since 2004 to more than $43bn a year.

It is against this backdrop that the two leaders are expected to explore areas of mutual interest, including Afghanistan, global climate change, the development of green energy, agricultural co-operation and enhancing Indian education.

“The big picture in Washington is that China and India are rising and the Obama administration wants to engage them both to help solve the world's problems,” said David Rothkopf, a former official in the Clinton administration, which paved the way for Mr Bush's Indian charm offensive.

Mr Singh's trip is the first full state visit of the Obama administration, with a White House dinner tomorrow to be attended by 400 guests, and is the first time India has headed a US president's list for a state visit. But diplomatic pageantry will not be sufficient to assuage Indian concerns about Washington's broader strategic vision, especially after last week when Mr Obama and Hu Jintao, the Chinese president, jointly affirmed their commitment to work for stability in the “south-Asia region”.