With the New START treaty ratified, the Obama administration can turn its attention to the real source of nuclear instability among the great powers: China's buildup of conventional ballistic missiles. The latest destabilizing system is China's anti-ship ballistic missile, the "carrier killer" that the head of the U.S. Pacific Command, Adm. Robert Willard, deemed operational last week.

During the many upcoming Sino-American summits, including a state visit by President Hu Jintao, the Obama administration should begin pressing China to join the Intermediate Nuclear Forces (INF) Treaty and stop its missile buildup.

Why are China's missiles the greatest source of unease? Because there are no defensive answers that do not risk an immediate escalation of tensions - and Beijing's missile force is soon likely to have the ability to ground Pacific-based U.S. air forces and sink surface ships in Asian waters.

China has the world's most ambitious missile modernization program. The anti-ship ballistic missile program that Willard identified is one of many Chinese advances; others include mobile multiple independently targetable (MIRV) intercontinental ballistic missiles, hypersonic post-boost vehicles that remain in the atmosphere and preclude intercept in flight, and a new generation of extended-range, ground-launched land attack cruise missiles. No missile defense program on the horizon is capable of intercepting these systems.

Over the past decade China has claimed that it needed to expand its missile force because of ongoing tensions with Taiwan. Relations with Taiwan have warmed, yet Beijing's missile buildup continues. While there is little doubt that Chinese nationalists want to force Taipei into a settlement, it now appears that the Taiwan issue also served as a justification for a massive missile modernization program. For China, a missile-centric military strategy makes sense: Defending against sophisticated ballistic and ground-launched cruise missiles is extremely difficult, and, unlike the United States and Russia, China is not a signatory to the 1987 INF treaty, which precludes only Washington and Moscow from deploying short and intermediate range land-based ballistic and cruise missiles.

By building a missile force second to none, China is increasing its capability to coerce its neighbors into resolving political disputes on its terms and the costs of a U.S. response. But the expansion of China's missile force both undermines regional security and exacerbates a classic regional arms race. The only real defense against these weapons is offense, so countries threatened by China's missiles will seek the ability to target the infrastructure supporting missile launches within nuclear-armed China. India and Taiwan are investing in precision strike systems heavily reliant on missiles. Over time, Japan may feel compelled to deploy its own ballistic and cruise missiles.

More ominous still is that China's missile buildup could result in the INF's demise. Moscow has already threatened to pull out if China does not sign the treaty. And, with its tactical fighter bases and surface ships increasingly vulnerable, the United States also may have no choice but to abrogate the treaty and deploy mobile land-based missiles - a capability much more difficult for China to attack - to places such as Japan; this could become the only way to deter Chinese aggression. The end of the INF would mean a missile arms race involving four great nuclear powers - India, China, Russia and the United States. Without sustained attention to China's missile force this frightening scenario is becoming more plausible.

Even absent a ballistic missile competition among the great powers, strategic stability in Asia is increasingly uncertain. If Washington remains bound by the INF, its response options in a conflict with China are highly escalatory. If U.S. tactical fighter bases and surface ships were hit by Chinese missiles, Washington would have to consider responding by targeting missile assets inside China with intercontinental ballistic missiles. To do so, Washington will need to further develop its Prompt Global Strike system, a means of accurately launching long-range missiles from the continental United States. Because such missiles could also be used to carry nuclear weapons, Chinese defenders would have no way of knowing whether the munitions flying toward them were carrying nuclear or conventional warheads. This uncertainty raises the risk of a Chinese nuclear response.

China's unrelenting deployment of missiles will soon force Washington to choose between pulling out of the INF or developing longer-range, strategically unstable military responses that are consistent with the agreement. If Washington is serious about reducing the risk of nuclear conflict, it should pursue a third option - pressing China to join the treaty. Failure to do so will quickly make New START irrelevant to nuclear stability.

Mark Stokes, executive director of Project 2049 Institute, served in the U.S. Air Force for 20 years. Dan Blumenthal is director of Asian studies at the American Enterprise Institute.