THE new sourness between India and Pakistan has begun almost in farce, but that conceals a serious deterioration.

For those looking for pockets of optimism in an unstable world, that is dismaying. The warming-up of relations between the two nuclear-armed neighbours in the past two and a half years has been indisputable good news. The US has contributed to this deterioration, albeit with good intentions. It has chosen to court India with poorly thought-out concessions on its nuclear programme, and Pakistan with a package of treats, including arms sales. America’s engagement should be welcomed, but these are favours the region could have done without, while Washington has ducked any attempt to help the rivals to settle the border dispute.

In the latest row India has expelled a Pakistani diplomat in retaliation for the expulsion of an Indian visa official allegedly caught spying. This is hardly the first set of mutual expulsions since independence from British rule in 1947. The neighbours have resorted to this so often that there is an element of comedy (although the Indian diplomat in question claims he was roughly treated, something Pakistan denies).

But this was the first expulsion since the new peace process began in January 2004, when the two countries began to try to normalise relations and to resolve their dispute over the Himalayan region of Kashmir.

They were taking some steps forward, although very slowly. They had opened bus routes across the border. Trade was picking up, from vestigial levels. But they had made little progress on the central issue of Kashmir, the subject of two of the three wars they have fought since independence.

The July 11 attacks on Bombay commuter trains, which killed 207 people, halted talks. India, which blamed Islamic militants operating from Pakistan-controlled Kashmir, called off meetings due on July 21 and this month, although Pakistan denied culpability.

The peace process is not dead. The foreign secretaries of both countries have met since then at a regional summit and pledged to press ahead. Ministers will also meet again at the United Nations General Assembly next month in New York. “They will definitely not be going to a pre-2002 situation,” Najam Sethi, the Lahore-based editor of the Daily Times newspaper, said, referring to the crisis during which a million troops poured on to the disputed border. But he added: “Definitely the peace process is getting into difficulties” — a point with which Indian analysts heartily agree.

But the Bombay bombings were not the first cause of trouble. The deal that the US has signed with India, to help it to develop its civilian nuclear industry, has provoked huge controversy in the US Congress as well as in the region. It could allow India to make a big leap in military capability, while the US did not insist that India sign the nuclear Non-Proliferation Treaty in return.

Many feel that the deal undermines the strength of that treaty at a time when the West wants Iran, a signatory, to curb its nuclear ambitions. Congress has not yet given its backing.

At the same time the US has pressed ahead with arms sales to Pakistan. Having decided that President Musharraf is a key ally in the War on Terror, it has chosen to overlook all kinds of provocation. Never mind Pakistan’s refusal to let the US interview its scientist A. Q. Khan, who helped Iran, North Korea and Libya to acquire nuclear technology. The US has also been willing to allow Pakistan to play down revelations last month of a partially completed heavy-water reactor, saying the new facility will produce far less plutonium than reports had suggested.

The Clinton Administration made some attempt to engage both sides in discussions about whether the future border through Kashmir would lie along the so-called line of control. The weakness of the Bush Administration’s tactics is that it doles out favours to both sides while avoiding the heart of the problem that divides them.

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