The British Opposition leader, Mr William Hague, drew Labour and Liberal Democrat fire last night after pledging that a Conservative government would back US plans for a new "Son of Star Wars" missile system.
The British Defence Secretary, Mr Geoff Hoon, accused the Tory leader of trying to make political capital out of "a very sensitive" international issue.
"It is typical of William Hague to go blundering around regardless of the sensitivities, and showing no judgment or sense of responsibility," declared Mr Hoon.
Mr Menzies Campbell, the Liberal Democrats' spokesman, said: "It takes a particular kind of naivety to endorse a system which has so far failed every test." Too much of the Tory language, he said, was reminiscent of the Cold War "as they try to prove they are Thatcher's children".
But Mr Hague clearly senses he had ministers on the defensive over an issue Tories believe spells potential difficulty and division for the Prime Minister, Mr Blair - both within the Labour Party and between the British government and its European partners.
Downing Street said it was not required to have a position since no firm US proposals had yet been advanced.
In a speech to the American Enterprise Institute in London, Mr Hague renewed his commitment to keep the new European Rapid Reaction Force firmly under NATO control, and warmly embraced the plan for a missile shield to protect the US and its allies from attack by "rogue" states such as North Korea, Iraq, Iran and Libya.
The £40 billion project is fiercely opposed by powers including China and Russia, who protest that it breaches the 1972 Anti-Ballistic Missile Treaty. The plan would require extensive updating at the early warning station at Fylingdales on the North Yorkshire moors. Mr Hague said: "Some British opponents seem to want to resist the upgrade at Fylingdales. They think thay can deflect America from its chosen course. Such a view is foolish and naive.
"If consent for changes at Fylingdales is withheld, the world's one remaining superpower will not just give up its fundamental objectives. It will find other ways of pursuing its aims. And the relationship between Britain and America will have suffered a most serious blow."
The shadow defence secretary, Mr Iain Duncan Smith, defended Mr Hague against Mr Hoon's criticisms. "In its heart the Labour Party is still at the wire at Greenham Common and Tony Blair is still wearing his CND badge," he said.