Campaigners are hoping the controversial American Missile Defence system could be stopped after the shock defection of an American Republican Senator.
James Jeffords' decision to become an Independent gave the Democrats control of the US Senate.
They pledged immediately to moderate the policies of President George W Bush while taking the chance to advance their own.
"I can no longer remain a Republican," said Senator Jeffords said in a personal declaration of independence.
His announcement was immediately welcomed by opponents of Bush's "Son of Star Wars" defence programme, which would include RAF Fylingdales, on the North York Moors, in a system designed to shoot missiles from the sky.
Bill Shaw, York's Green candidate in the General Election, said: "Senator Jeffords could have become the man who saved the world."
Updated: 11:01 Friday, May 25, 2001
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