Senate Republican conservatives signaled yesterday that they will demand a vote next week on the Comprehensive Test Ban Treaty, complicating efforts by Senate leaders to avert a showdown that would likely result in rejection of the pact.

Under an agreement scheduling the vote, a single senator can block its cancellation, and several said they would do so unless President Clinton takes the initiative to shelve the treaty, one of his major foreign policy priorities.

Some were prepared to insist on a vote regardless of what Clinton does. Sen. James M. Inhofe (R-Okla.) announced he will demand a vote, and Sens. Tim Hutchinson (R-Ark.) and Robert C. Smith, a Republican-turned-independent from New Hampshire, joined Inhofe in signing a letter to that effect.

The maneuvering started after Republicans, who had delayed action on the treaty for two years, responded to Democratic pressure for a vote by scheduling it for next Tuesday or Wednesday. But then leaders of both parties decided to try to find a mutually acceptable way of avoiding a vote that many senators feared could damage U.S. prestige, encourage nuclear proliferation and boomerang at the polls next year. The problem is that each side wants the other to take the first step.

As the day began, Clinton indicated he could accept a postponement to avoid what both parties describe as almost certain defeat. But he refused to ask for it, and Democrats said neither they nor Clinton could accept conditions being sought by Republicans.

"If senators, in their wisdom, believe they need more time, they need more months to look at this, then we will certainly be open to looking at their concerns," White House press secretary Joe Lockhart told reporters. "Again, they have the power in the Senate to set the schedule to bring this on the floor on a day that they agree." He repeatedly said one week was insufficient time to debate the treaty's merits.

Majority Leader Trent Lott (R-Miss.) has said he is willing to consider canceling the vote if Clinton agrees not to seek a vote on the treaty before he leaves office in January 2001. Foreign Relations Committee Chairman Jesse Helms (R-N.C.) said he also would insist that Clinton request withdrawal of the treaty in writing. Armed Services Committee Chairman John W. Warner (R-Va.) put it more gently, saying Clinton "must share with the Senate leadership the burden of not going forward."

Many senior Republicans have urged that the vote be put off. "We're not testing now. What's the rush?" said Sen. Ted Stevens (R-Alaska), arguing that more time is needed to develop alternative means of testing the viability of the nation's nuclear stockpile.

But Inhofe said the treaty should be rejected now on its merits.

While there were no negotiations yesterday, both sides said an agreement to cancel the vote remains possible. But both sides continued to make their cases for and against the treaty.

The treaty received a major boost from the military when Army Gen. Henry H. Shelton, chairman of the Joint Chiefs of Staff, said the chiefs unanimously favored ratification. "The world will be a safer place with the treaty than without it, and it is in our national interest to ratify the CTBT treaty," he told the Armed Services Committee.

Treaty opponents countered with a letter from six former defense secretaries from Republican administrations opposing the pact on the grounds that it would "reduce the credibility of America's nuclear deterrent."

Appearing with Shelton, Defense Secretary William S. Cohen was lukewarm about shelving the treaty while the United States continues the moratorium on testing it adopted in 1992. Noting that some senators do not want to ratify the pact, but do not want to reject it either, Cohen said, "In that case you have a moratorium, but no disincentive for other countries not to test."

If other nations develop nuclear capability, he said, the United States might be forced "to review our own deterrent requirement" and perhaps return to full-scale testing and production of nuclear weapons.

At a White House ceremony, Clinton made a 20-minute appeal for the treaty.

"The best way to constrain the danger of nuclear proliferation and, God forbid, the use of a nuclear weapon, is to stop other countries from testing nuclear weapons," he said. "That's what this test ban treaty will do. A vote, therefore, to ratify is a vote to increase the protections of our people and the world from nuclear war. By contrast, a vote against it risks a much more dangerous future."

Staff writer Charles Babington contributed to this report.