If the Senate eventually fails to ratify the Comprehensive Test Ban Treaty, there will be another victim besides the one Senate Republicans intended. For it is not only President Clinton who will be harmed by the action but the person who takes office as president--and many Republicans presume it will be one of their own--in 2001. The new president will face nuclear shock waves around the world, bereft of bipartisan support when he most needs it.

Here are some likely scenarios:

* India will probably conduct more nuclear weapons tests. India's nuclear scientists and hawkish strategists want a sophisticated arsenal, ranging from small tactical weapons to huge hydrogen bombs. They also wish to overcome doubts about the technical performance of the weapons tested in May 1998. More tests would satisfy them and their potential military "customers" that they can mimic the great powers.

Conversely, ratifying the test ban treaty would tether the nuclear hawks and allow India to concentrate on the economic route to major powerdom. India's leading statesmen, Prime Minister Atal Bihari Vajpayee and Foreign Minister Jaswant Singh, recognize this and want to avoid a costly and dangerous arms race. A Senate rejection of the test ban treaty would undermine these statesmen and badly complicate increasingly vital U.S.-Indian relations.

* Pakistan would match India test for test. This would lead to the kind of arms race that Presidents Reagan, Bush and Clinton have sought to block in the subcontinent. Lest an arms race seem inconsequential, it should be recalled that India and Pakistan just battled in Kashmir. The fighting came closer to erupting into an all-out war and possible nuclear escalation than was reported. If more testing occurs and hawks in both countries are unleashed, defense spending will increase. Pakistan will move closer to bankruptcy. This will heighten the risk of Taliban-like groups gaining power in Pakistan, metastasizing cells of intolerance, aggression and anti-American terrorism that would bedevil the next American president.

* While China has signed the test ban treaty, it will not ratify it if the United States doesn't. China assumes that rejection means Republicans want to conduct more nuclear tests; otherwise, why wouldn't they ratify? In this case, China will make preparations to resume nuclear testing, especially if India conducts more tests. China possesses only some 20 long-range, single-warhead missiles capable of striking America. This poses no serious threat to the U.S. deterrent. China has conducted some 45 nuclear explosive tests, the United States 1,030. The test ban is valuable precisely because it constrains the kind of weaponry advances that the Chinese military might otherwise wish to make with purloined American design information.

* Japan will face pressure to reconsider its nuclear abstinence if China and India build up nuclear forces. Test ban opponents in Washington argue that American ballistic missile defenses should reassure Japan that it does not need to hedge its bets. However, the Japanese, like U.S. allies in Europe, recognize the technical and strategic problems posed by inevitably less-than-perfect defenses. Indeed, Senate rejection of the test ban paired with aggressive promotion of ballistic missile defenses will prompt China and Russia to feel that the United States is bolstering its capacity for nuclear coercion and possible first use. Moscow and Beijing will augment their nuclear offenses to counter defenses. In this context, Japan (and NATO allies) will feel more rather than less threatened. The next American president could then confront a crisis in alliance relations.

* Globally, rejection of the test ban will endanger the nuclear nonproliferation regime. In 1995 the international community agreed to extend indefinitely the Nuclear Non-Proliferation Treaty on the promise that the nuclear weapon states would complete a test ban treaty by 1996. This was the minimal disarmament condition that the world would accept from the United States and the other nuclear states. The 187 parties to the nonproliferation treaty will meet next April to review the status of the treaty. If the Senate rejects the test ban, we can be sure that measures to tighten nonproliferation controls and maintain sanctions on Iraq will be opposed by an outraged international community. Instead of being the champion of nonproliferation, the United States will be seen as the rogue state of proliferation.

Again, isolationists may say, "Who needs the nonproliferation regime? If we feel threatened by proliferation, we can take care of it ourselves." But the U.S. interest in keeping countries such as Iran from acquiring nuclear weapons requires cooperation from states such as Russia and our European allies in controlling exports. Washington's persuasive powers will be seriously undermined by roguish behavior on the test ban treaty.

Republicans in the Senate who want both to defeat the test ban and elect a Republican president should be careful what they wish for. If they reject this treaty they will create conditions that no new president could welcome. Given that the United States could ratify the treaty and still legally escape from it if a threat to national security emerged, the next president would likely wonder, "Whose idea was this?"

George Perkovich is the author of "India's Nuclear Bomb," to be published next week.