The rejection of the Comprehensive Test Ban Treaty is indeed a debacle for American foreign policy, but the blame lies with the Clinton administration rather than with the Republican-led Senate.

This is the first time in modern history that the United States has failed to ratify a major arms control agreement, a development that has unsettled allies in Europe and Asia, while making Washington an easy target of criticism for Moscow and Beijing.

While President Clinton has already claimed that isolationists in the Senate are responsible for the outcome, there is more than enough blame to go around. Indeed, the vote is principally the product of two major mistakes committed by Clinton and his senior advisers.

The first is the administration's failure to methodically build a bipartisan consensus for the complicated and controversial treaty.

While U.S. administrations going back to the Eisenhower era have given lip service to the goal of a negotiated ban on all nuclear testing, in practice they proceeded cautiously in trying to achieve this goal. This is because a test ban raised some difficult technical challenges that needed to be surmounted before Senate approval.

One such challenge was whether the United States, with a military strategy based on credible nuclear deterrence, could maintain a highly reliable stockpile of nuclear weapons indefinitely without testing. Another challenge was how to ensure that a test ban could be verified and enforced: Could we catch cheaters, and if so, how would they be penalized by the international community?

In last week's debate, these questions were still at the forefront of the debate, and it was clear that many senators had doubts about the administration's answers.

The outcome might have been different had the administration paid attention to how the Senate was handled during the Reagan-Bush era, when three major arms control treaties were negotiated and ratified, including the 1991 accord reducing U.S. and Russian strategic forces by half.

The lesson from this period was simple but important: In any arms negotiation, if you want Senate support at the landing, you had better arrange for heavy Senate involvement at the takeoff.

Accordingly, bipartisan teams of Senate "observers" regularly visited key arms control negotiations during the 1980s, consulting with not only American negotiators but also with diplomats across the table. Between these visits, Reagan and Bush aides kept senators informed on the course of the talks.

Of course, this intensive process sometimes complicated -- and even prolonged -- negotiations. For example, during negotiations covering strategic arms reductions, it became apparent that several senators had doubts about the adequacy of the evolving plan for missile inspections. Accordingly, U.S. negotiators were instructed to upgrade the accord's procedures for verification.

Strangely, the administration ignored this experience in the case of the test ban treaty. Potential Senate critics were shut out of the negotiations, and treaty proponents were given only last-minute support. For a White House supposedly adept at political management, it was an episodic and halfhearted effort at best.

The second key mistake was conceptual: The administration failed to provide a compelling rationale for a test ban in the changed circumstances of the post-Cold War era.

With the collapse of the Soviet Union, nuclear competition between Washington and Moscow has ceased to be a central concern. At the same time, the spread of nuclear arms to new nations has become an increasingly worrisome trend.

But it is unclear how a test ban would curb nuclear proliferation. In the bipolar international system of the Cold War, nations took their cue on nuclear matters from the two superpowers. In the increasingly fragmented and decentralized world of the 21st century, nations such as Iraq and North Korea refuse to follow Washington's lead. Pakistan and India, which have acquired nuclear arsenals despite concerted opposition by the United States and others, are cases in point.

Like some earlier accords, such as the 1972 American-Soviet agreement curbing antimissile defenses, the test ban treaty represents an anachronistic approach to arms control. Despite numerous complaints, however, the Clinton administration has insisted on pursuing an outmoded agenda unsuited to a new security environment.

Last week's fiasco in the Senate underscores that effective arms control requires both political commitment and policy coherence. In the case of the test ban treaty, the administration has demonstrated little of either.

The writer was the chief U.S. negotiator in the Strategic Arms Reduction Talks during the Bush administration.