With the defeat of the Comprehensive Test Ban Treaty yesterday, the U.S. Senate has shattered the centerpiece of the Clinton administration's arms control strategy, and diplomats and arms experts warned that the worldwide fallout could be severe and long-lasting.

The most immediate impact, experts said, might be to undermine the ability of the United States to persuade India and Pakistan to sign the test ban treaty, a campaign the Clinton administration has been waging since the two Asian foes conducted tit-for-tat nuclear weapons tests early last year.

The longer-term effect could be to undermine the ability of the world's leading nuclear power -- the United States -- to limit membership in the nuclear weapons club, stop nuclear development by Iran and North Korea, and persuade Russia and China to keep lids on their arsenals.

"The initial impact will be catastrophic in terms of the U.S. ability to be taken seriously in international efforts to control the spread of nuclear weapons," said Rebecca Johnson, editor of Disarmament Diplomacy and head of a London-based think tank that monitors arms talks. "The signal the rest of world gets is that the United States prefers to engage in playground partisan politics rather than working with its allies on collective efforts at international security."

Even opponents of the treaty conceded that the immediate effect of its defeat would be negative. "When we have staked so much on such a treaty, it reflects badly on our leadership," said former secretary of state Henry A. Kissinger, who favored a delay in the vote. "On the other hand, I think it's a bad treaty."

Since 1968, efforts to stop the spread of nuclear weapons have been based on a fundamental bargain, according to Thomas Graham, a former arms control negotiator who is now president of the Lawyers Alliance for World Security.

"Most of the world agreed never to acquire nuclear weapons, and the five nuclear states agreed [in return] to pursue disarmament negotiations aimed at the ultimate elimination of nuclear weapons," said Graham, adding that non-nuclear nations "looked at the test ban treaty as the litmus test of the sincerity of nuclear weapons states living up to their half of the bargain."

In 1995, when the Clinton administration twisted diplomatic arms to win a permanent extension of the nuclear Non-Proliferation Treaty, it agreed to push hard for ratification of the test ban. "For the Senate to reject it now would be regarded as bad faith by many of those states around the world which only reluctantly agreed to make the Non-Proliferation Treaty permanent," said Graham, who was involved in the negotiations.

Secretary of State Madeleine K. Albright tried early yesterday to contain the damage from the anticipated Senate vote. "The United States today has no plans and no need to conduct nuclear explosive tests," she said. "It is plainly in our interest to discourage others from doing so as well."

And Kissinger said many experts have overstated the impact of the treaty's rejection. "Other countries, whether we sign the treaty or not, will have to take seriously our negative attitude toward testing," he said.

But among many European allies, the defeat of the treaty was viewed as the gravest abdication of American leadership on arms control in the post-Cold War era.

"I think the effect will be disastrous both psychologically and substantively," said one European diplomat.

"This is not just a dangerous signal, it is a declaration of our own stupidity," argued a U.S. ambassador in Europe.

In Russia, President Boris Yeltsin has not yet submitted the test ban treaty to the parliament. "The delay in the United States will cause delay here," predicted Alexander Pikayev, an arms control specialist at the Carnegie Endowment Moscow Center. "If the United States ratified the treaty, I am sure Yeltsin would have submitted it for ratification, but now it is shelved, so it is not clear when, and whether, that happens."

Pikayev said, however, that he doubted Russia would resume testing. He noted that at a Kremlin security council meeting in April, a decision was taken to try to improve mathematical simulations of nuclear explosions, indicating that Russia intended to adhere to the ban as long as others did.

The defeat in the Senate came just as the Clinton administration was hoping to secure India's signature on the test ban treaty. India had said it would sign after its elections, which took place earlier this month, and Pakistan, now shaken by a military coup, had said it would sign if India did.

Yesterday, however, a senior Indian official said that the test ban is a "treaty whose time may never come."

"I think the [Indian Prime Minister Atal Bihari] Vajpayee government is committed to signing because there is a lot riding on its relationship with the United States," said Ashley Tellis, an expert on South Asia at the Rand Corp. "But it will be very difficult for them to go to their domestic constituency and say they ought to be signing a treaty that the U.S. Senate in all its wisdom has rejected."

Pakistani officials said the Senate action bolsters their long-standing contention that it is the world's five major nuclear powers -- the United States, Russia, China, Britain and France -- that pose the greatest threat to the spread of nuclear weapons. But they said Tuesday's coup makes it impossible to predict how their government will react to the Senate's decision.

"At this point we have other concerns on our minds," said one Pakistani diplomat.

Correspondents David Hoffman in Moscow, William Drozdiak in Berlin and Colum Lynch at the United Nations contributed to this report.