During the Cold War India was the only major democracy in the world that did not side with America in the struggle against communism. But in the past decade, driven by India’s rapid economic growth, a shift in American priorities in Asia and, latterly, the demands of the war on terrorism, the interests of the two countries have converged sharply.

With US global hegemony increasingly challenged by the rise of China, India — with a population of more than a billion — is seen by many in Washington as a natural and vital strategic ally. Mr Bush arrives in India on Wednesday and will spend three days there before visiting Pakistan, also for the first time, where he will hold equally critical discussions with General Pervez Musharraf, the President.

American expectations are high for both legs of this trip, but especially for Mr Bush’s meetings with Manmohan Singh, the Indian Prime Minister.

“The President’s visit, at least to some extent, marks the transition from a 40-or-so-year painful bilateral history to the transformed relationship the two countries have today,” Robert Blackwill, a former US Ambassador to India, said last week.

The change in the relationship is reflected in that India is, according to recent surveys, the one place where the popularity of the US, if not its President, has risen in the past four years.

American officials cite many areas of common interest. As Mr Bush presses a pro-democracy agenda for the world, India is the world’s largest free nation. Economic growth in the sub-continent has been rapid, bringing trade and investment opportunities for both countries’ companies.

The two countries have shared interests in energy security and, of course, in confronting Islamist extremism. And, in the US at least, some long-term strategic thinkers see India — democratic, capitalist and, in large part, English-speaking — as a powerful ally and makeweight to China’s growing hegemony in Asia, although Indian officials, eager to stay on good terms with their large neighbour to the north, are keen to play down that aspect of the relationship.

Mr Bush and Mr Singh will discuss those issues, and India’s relations with Pakistan, where a fledgling peace process is under way over the disputed territory of Kashmir.

But the most important item on the agenda may also be the most contentious. In 1998 Delhi became a member of the nuclear weapons club, in defiance of the global non-proliferation treaty. For Washington, in its increasingly urgent efforts to halt the spread of nuclear weapons, this continues to represent a serious challenge.

But last July, when Mr Singh visited Washington, the Administration agreed to assist India with its civil nuclear energy programme, despite opposition in the US Congress. Before the deal could be finalised, however, India had to agree to demonstrate clear separation between its civil and military nuclear facilities.

This has proved difficult, and so far the proposal has satisfied nobody. The Opposition in India sees it as an attempt by Washington to impose limits on India’s nuclear weapons capabilities. US critics say that it does not go far enough to limit India’s military nuclear programme. Officials on both sides were still working on the details at the weekend — hopeful that the final agreement would be ready for Mr Bush to sign this week.

US relations with Pakistan, where Mr Bush will spend next weekend, have also been transformed in the past few years, though in this case by the pressing issue of terrorism.

General Musharraf’s Government has been persuaded to drop its long-standing support for Islamists in Afghanistan, including its old allies the Taleban, and join the US in fighting al-Qaeda and its associates.

With growing evidence that the war against Islamists in Afghanistan is faltering, not least because former Taleban and al-Qaeda members are working unmolested in Pakistan, Mr Bush will seek a renewed Pakistani effort against Islamic militancy — a tricky proposition for General Musharraf, whose support for the US is deeply unpopular.

Mr Bush will be on his best diplomatic behaviour, emphasising the emollient new tone of his second term. The US team has even arranged for him to spend some time on a subject of vital significance to both Indians and Pakistanis, though incomprehensible to Americans. He told Indian journalists in Washington last week: “As I understand it, I may have a little chance to learn something about cricket. It’s a great pastime. ”

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