An article Friday incorrectly said the Comprehensive Test Ban Treaty was negotiated in 1966. It was negotiated in 1996. (Published 10/05/1999)

Senate Republican leaders yesterday abruptly reversed course and proposed votes next week on a treaty to ban all nuclear testing, abandoning their delaying tactics in favor of a showdown they believe will result in defeat for the treaty.

After weeks of pushing for an early vote, administration officials and Senate Democrats were hard-pressed to reject the offer, even though they conceded they do not have anywhere near the two-thirds majority needed to ratify the pact.

The 1966 Comprehensive Test Ban Treaty has become a priority for the administration and many Democrats, who argue that, with the United States already having stopped testing, the pact would preserve U.S. nuclear superiority while discouraging nuclear proliferation in the rest of the world.

But many Republicans contend that it would bar the United States from modernizing its arsenal to cope with nuclear threats from other countries that may not sign or ratify the pact and endanger national security, especially so long as this country has no national missile defense system.

After several days of behind-the-scenes strategizing, Majority Leader Trent Lott (R-Miss.) proposed to bring up the treaty next Wednesday, with a vote after 10 hours of debate. Minority Leader Thomas A. Daschle (D-S.D.) protested the short notice, lack of hearings and one-day debate limit but indicated he was willing to work out a plan for voting later in the month.

Some Democrats, including Sen. Joseph R. Biden Jr. (Del.), the party's ranking member on the Foreign Relations Committee, said they would take the vote in order to put senators on record on the issue and build public support for it. If it is defeated, Biden and others said they intend to keep bringing it up for a vote. He also said he will call on President Clinton to undertake a public crusade for ratification.

As of late yesterday, Democrats were still trying to negotiate changes. But an aide to Foreign Relations Committee Chairman Jesse Helms (R-N.C.) called the earlier offer a "take-it-or-leave-it" proposition.

Lott's move followed stepped-up pressure over the past few weeks by the Clinton administration for action and almost daily accusations from Democrats that GOP leaders were dragging their feet in bringing the pact to a vote.

It also appeared to reflect nose-counts indicating that test ban supporters, mostly Democrats, are about 15 votes short of the two-thirds vote required by the Constitution for ratification of treaties. Even with all 45 Democrats voting for the pact, they would need the support of 22 Republicans. Biden indicated to reporters he could count only about seven Republicans.

Administration officials fear the treaty will be defeated if Lott makes it a test of party discipline for Republicans, but they also said there seem to be enough undecided senators to give the treaty a chance. They cited recent polls showing it has bipartisan support among voters.

State Department spokesman James P. Rubin said the administration wants the treaty ratified as soon as possible but "we have concerns that the current schedule is not going to allow the kind of serious debate and consideration that a treaty of this critical importance merits."

During yesterday's brief debate, Lott made it clear he opposes the pact. "I think this treaty is bad, bad for the country, and dangerous," he said, "but if there is demand that we go forward with it, as I have been hearing for two years, we are ready to go."

Republicans seemed to enjoy the Democratic response, especially Daschle's objection to prompt votes on a treaty he supports. After "incessant grandstanding" for a quick vote, "the same people clamoring for action go running for the hills," Helms said. "If it were not so pitiful, it would be amusing."

The treaty, negotiated between 1964 and 1966, would commit all countries that sign it to refrain from any kind of nuclear testing and set up a monitoring system to assure compliance. It has been signed by 154 countries, including the United States, which was the first to do so. But it has been ratified by only 47 countries, including only 23 of the 44 nuclear-capable countries that must ratify it before it can take effect. Three such countries--India, Pakistan and North Korea--have not signed the treaty. Russia and China have not ratified it and, according to Biden, are waiting for the United States to act first.

Treaty supporters were pushing for an early vote in part because a conference will be held in Vienna Oct. 6-8 to consider how to get nonsignatory countries such as India and Pakistan to sign on.

Staff writer Steven Mufson contributed to this report.