BBC Washington correspondent Richard Lister: "Not enough conservatives seem to be prepared to ratify"

The revelation comes after the US Central Intelligence Agency concluded that it was unable to accurately monitor low-level tests at a key site in the Russian Arctic.

The issue has come to a head because the US Senate is considering ratification of a Comprehensive Test Ban Treaty (CTBT), which Senate conservatives say should be rejected because of verification problems.

The United States and Russia are among the more than 150 signatories to the CTBT, but neither has yet ratified it.

President Clinton has promised an all-out fight to get the treaty ratifiied by the Senate.

The BBC's Alix Kroeger reports: "Clinton says he'll do all he can"

"It is strongly in our interest to achieve agreement that can help prevent other countries like India, Pakistan, Russia, China, Iran and others from testing and deploying nuclear weapons," he stated.

Arctic testing

US Energy Secretary Bill Richardson - visiting Moscow at the weekend - proposed to his Russian counterpart Yevgeny Adamov that Moscow gives US experts access to the Novaya Zemlya nuclear test site in the Arctic.

Such visits would help the United States distinguish between nuclear testing and other seismic activity like earthquakes.

Mr Richardson also suggested that Moscow give Washington 24 hours notice before conducting low-level reliability tests of existing weapons, which is allowed under the treaty.

The Russian energy minister is reported to have been willing to discuss such access, but said in return Russia should be given American computer technology which allows simulated nuclear testing.

A CIA report said the agency could not monitor low-level nuclear tests by Russia precisely enough to ensure compliance with the CTBT.

In September, the Russians twice conducted what might have been nuclear explosions at the Novaya Zemlya test site, according to US officials quoted by the Washington Post.

But the CIA found that data from seismic sensors and other monitoring equipment were insufficient to allow analysts to reach a firm conclusion about the nature of the events.

Congress

The CIA report could further undermine the CTBT's already poor chances of winning the two-thirds majority it needs to be ratified by the Senate, where its Republican opponents hold a 55-45 seat advantage over Democrats.

Senator Trent Lott decided to call a debate on the CTBT

Senate Republican Majority Leader Trent Lott last week suddenly offered to hold a vote on the test ban treaty after having refused to bring it to the floor since President Clinton sent it to the Senate for ratification two years ago.

The vote is expected on 12 October.

No Indian tests

A new Indian Government led by Prime Minister Atal Bihari Vajpayee's Bharatiya Janata Party would be ready to sign the CBTB, Mr Vaypayee's national security adviser Brajesh Misra said on Sunday.

India was widely criticised along with Pakistan for conducting nuclear tests last year, after which President Clinton cancelled a visit to the region, now due early next year.