THE claim by sources in Washington that Teheran is pursuing a secret nuclear-weapons programme is both credible and alarming. Iran is hardly a member of the family of nations, and while Teheran has little to lose in terms of friendships, nuclear weapons would certainly add a little weight to the country's influence in military terms. It is no coincidence that states with nuclear capabilities or ambitions tend to be found in volatile regions. For Iran, the temptation must be strong to seek a nuclear capability when Iraq is on its knees. When any nation pursues such a programme, the rest of the world should act swiftly and in concert to underline the price of nuclear ambition. In the case of Iran, it strains credibility to suggest Russia had no idea that the nuclear technology it was supplying might be turned to military purposes. Even allowing for Teheran's legitimate needs in terms of power generation, Moscow should have smelt a rat when it won a US$1 billion contract to build up to four reactors. Russia is on the ropes economically and politically, and may have initially regarded the Iranian contract as a gift horse. However, Russia would be storing up potential problems for itself if it helped - even unwittingly - in the development of nuclear weapons in Iran, with which it shares a border. Washington is wise to try to shut the stable door now, before Moscow becomes irrevocably committed to the project. It is also fair that the United States should offer to compensate Russia for some of the losses it would face in abandoning the contract with Iran. While nuclear non-proliferation is in the interests of the whole international community, the US - committed to Israel and security in the Gulf, and alarmed at the spread of Islamic fundamentalism - should take the lead in halting the spread of nuclear weapons in the Middle East.