Washington correspondent Richard Lister: "Appeal had little influence on Republicans"

The plea came as the Senate looked increasingly likely to vote down the Comprehensive Test Ban Treaty (CTBT) which would ban all nuclear explosions.

UK Prime Minister Tony Blair, French President Jacques Chirac and German Chancellor Gerhard Schröder said rejecting the treaty would "expose a fundamental divergence within Nato" and encourage the spread of nuclear weapons.

"Failure to ratify the Comprehensive Test Ban Treaty will be a failure in our struggle against proliferation... Disarmament negotiations would suffer," the leaders warned in an article in the New York Times.

"For the security of the world we will leave to our children, we urge the United States Senate to ratify the treaty.''

Clinton appeal

Bill Clinton wants the vote postponed

But the appeal appeared to have had little success in persuading senators to change their minds ahead of the vote scheduled for Tuesday.

President Bill Clinton, who is desperately trying to save the treaty, on Friday urged the Senate to postpone the vote, rather than kill the treaty.

"I have asked them to put it off because we don't have the votes [to pass it]," he said.

"It is clear now that the level of opposition to the treaty and the time it would take to craft the necessary safeguards to get the necessary votes are simply not there."

Ratification, which requires a two thirds majority, is being blocked by the Republicans who dominate the Senate.

Critics say the treaty would constrain the US while allowing rogue governments to continue weapons development.

Mr Clinton made his appeal while in Ottawa for talks with Prime Minister Jean Chretien.

Mr Chretien remarked there were a lot of nations which had ''to live with the consequences" of what the US did.

Dramatic appeal

In Vienna, an international conference on Friday urged the US to ratify the document in the hope other countries would follow suit.

Delegates also appealed to India, Pakistan and North Korea to sign and ratify the treaty.

The CTBT has so far been signed by 154 states. To enter into force, it must be ratified by 44 states judged to have nuclear facilities. So far 26 have done so.

Those that have not include the US, Russia, China, India, Pakistan and Israel.

The conference, involving more than 90 countries, was held to look at ways of speeding up implementation of the 1996 agreement.

Ambassador Wolfgang Hoffmann, head of the watchdog body monitoring implementation, said Washington's leadership would be ''very helpful'' in encouraging others to follow.

Pakistan's ambassador at the conference warned a "massive nuclear arms race" could still erupt in South Asia due to what he said was India's lack of co-operation.