The terrorist attacks of Sept. 11 demonstrated this country’s critical vulnerability to homeland attacks — a vulnerability we have yet to address fully. Many do not realize how unprotected America remains to an aerial attack of another kind: ballistic missiles.

While the terrorists were able to utilize deficiencies in America’s overall approach to intelligence-sharing and aviation security, similar vulnerabilities exist in every infrastructure vital to the security, economy and survival of this nation: energy supplies, transportation and public health. A single ballistic missile could wreak devastation on a scale far greater than that of Sept. 11, and the only way to defend against such a threat is to incorporate a comprehensive missile defense system to intercept any such attacks.

The horrific events of Sept. 11 have proven beyond any doubt that terrorists will use any means at any cost to devastate the United States. With the proliferation of ballistic missiles in rogue states, the likelihood that terrorists and despots will use these weapons of mass destruction to attack American territory has grown substantially. Indeed, the terrorist attacks and threat of rogue regimes bolsters the case for fielding missile defenses sooner rather than later to protect Americans.

Yet opponents of missile defense seem to disagree with the President for two main reasons.

One, the cost. The Congressional Budget Office estimates that a limited land-based missile defense system could cost as much as $60 billion to develop, test and deploy. Yet this is a small price to pay for the nation’s security. Some opponents are hesitant to support missile defense because they fear its funding will cut into other immediate defense projects. But with the recently increased Pentagon budget, the war on terrorism will remain fully funded while missile defense receives its necessary funding for research and development. And other opponents fear increased defense spending will cause cuts in spending for domestic projects. It will — but this is a necessary cost.

Second, opponents question the feasibility of a working missile defense system because of technological limits. This is a valid concern, but the technology cannot advance without a massive investment in the research and development of such a system. With the recent success of last summer’s test, a fully operational missile defense system should be no more than a few years away.

Defending Americans is not an either/or proposition. Protecting the people, territory and institutions of the United States is the government’s first and foremost responsibility, and the U.S. military cannot ignore threats to security now that it is faced with a serious threat on the homeland. The United States needs a balanced national security policy that addresses the full array of threats to American lives, including the expanding threat posed by ballistic missiles.

As for arms-control agreements, they not only delay progress but undermine national security. Missile attacks will be far more destructive than the Sept. 11 assaults. Larger threats mandate more coherent and dedicated defense, not less.

The Cold War policy of “mutually assured destruction” spelled out in arms-control treaties is not sufficient to deter terrorist attacks. Cold War relics such as the 1972 Anti-Ballistic Missile (ABM) Treaty limit the ability of the United States to develop and deploy effective missile defenses. Proponents of arms control often argue that the United States will not face a missile attack in the first place because of the fear of overwhelming U.S. retaliation in kind.

The ABM Treaty thus makes a virtue of U.S. vulnerability, based on the belief that nations that value human life will not use their weapons of mass destruction if they face retaliation in kind. But this principle will not prevent terrorists supported by enemy regimes from acting, as so horribly demonstrated last Sept. 11. President Bush rightly has told the world that it is time to move beyond outdated paradigms to forge a new security environment — one not threatened by terrorists, enemy regimes, or the proliferation of weapons of mass destruction.

Homeland defense is meaningless without missile defense. While systems are now in place to thwart small-scale terrorism, the nation still has no defense against missile attack. Washington has no choice when it comes to defending Americans. Both terrorism and missile attack are growing threats to national security, and all such threats deserve comprehensive, dedicated and systematic responses.

Philip Shaw is a junior in Ezra Stiles College.