WASHINGTON -- Proponents of national missile defense are urging President-elect George W. Bush to move quickly to deploy a system to protect the United States against potential ballistic missile attacks from Iraq, Iran, North Korea and China.

They argue that he will make a major mistake if he lets his administration subject missile defense to a lengthy policy review. It will give opponents time to organize and inevitably entangle the issue in the 2002 congressional elections. Instead of waiting, Mr. Bush should seize the moment.

Mr. Bush could move ahead quickly and adopt the Clinton administration's missile defense deployment schedule, which proposes beginning construction of a key radar in Alaska next year. If Moscow refused to revise the ABM Treaty to permit a nationwide defense, the United States could then withdraw from the treaty. Although a momentous step, Mr. Bush could argue that he was merely following Bill Clinton's lead, and he might pick up Democratic votes in Congress as a result. By making deployment seem inevitable, Mr. Bush might overwhelm the domestic political opposition in the short term.

But from a longer-term perspective, rapid deployment is a bad idea. It could leave the United States with a mediocre missile defense, strained relations with most European allies and major problems with Moscow -- not to mention Beijing. American national security could suffer, particularly if a brusque defensive deployment led Moscow to terminate bilateral programs to secure its frighteningly dilapidated inventory of nuclear warheads and materials. Such an outcome would eventually fracture whatever domestic political support for missile defense the Bush administration had enjoyed.

Rather than moving quickly on missile defense, Mr. Bush should move sensibly. He should remain unwavering in his commitment to defending the United States.

But he does not need to commit immediately to a specific technology or to take steps that would violate the ABM Treaty until 2002, or perhaps even 2003. He has time to proceed deliberately for four reasons:

• The threat is limited. Only Russia and China currently threaten the United States with long-range missiles, and both could almost surely counter any defense now on the drawing boards. The threat from North Korea, Iran and Iraq is still probably several years off, or even longer. We should move purposefully on national missile defense, not hurriedly.
   

• The Pentagon needs time to research other technologies. The Clinton administration focused its efforts on developing a system to shoot down warheads in space. That poses a daunting technological challenge, as per the system's two recent test failures.

  The Pentagon has not adequately investigated other technologies, most notably boost-phase interceptors. These would shoot down enemy missiles before they reached space, when they were easy to locate and when they presented large targets. Besides being less technologically challenging than a Clinton-style system, boost-phase defenses are also far less vulnerable to countermeasures.

  It is not difficult, especially for a major country such as Russia or China, to build decoys that resemble actual warheads in the vacuum of space. But it's hard to hide or protect large, burning intercontinental rockets. Boost-phase defenses based on land, sea or air are also less likely to provoke Moscow. They must be based within a few hundred miles of the enemy missile launch point; hence, they cannot shoot down missiles launched from Russia's interior.
   

• The Bush administration needs time to negotiate changes to the ABM Treaty. Persuading Moscow to revise that 1972 treaty to permit nationwide missile defense is far preferable to abandoning it. Withdrawal would harm U.S.-Russian relations -- especially efforts to reduce and secure offensive nuclear arms in both countries.

  Even if Moscow says nyet in the end and the United States must withdraw, intensive negotiations would do more to assuage Moscow's worst-case security fears and to secure allied support for deploying a national missile defense than a capricious decision to abandon the treaty. But knowing in advance that Mr. Bush was firmly committed to deployment, and that he was also considering boost-phase defenses, Moscow might well agree to revise the treaty rather than face the prospect of unconstrained American national missile defenses.
   

• The Bush administration should work to find a way to defend the allies, too. The Clinton administration's proposed anti-missile system would protect the United States but not its allies. But leaving the allies unprotected seriously diminishes the system's strategic benefit. Saddam Hussein could blackmail us by threatening to destroy Paris or London or Tokyo -- including the thousands of Americans living there -- instead of New York or San Francisco.

Proponents of national missile defense are right that a Bush administration should be unyielding in its commitment to defend America. But that does not require immediate treaty-busting actions that favor unpromising defensive technologies. Acting resolutely should not mean rushing to failure.

James Lindsay and Michael O'Hanlon are senior fellows at the Brookings Institution.