The Sino-American relationship will be the most important bilateral relationship in the world during the next cycle of history, much as the U.S.-Soviet relationship dominated world affairs for most of the last half of the 20th century. Getting it right is vital for our national interests.

Almost ignored in the current focus on Afghanistan, the Middle East and homeland security is an unexpected opportunity to improve that relationship. Call it a chance to start Phase Three. It began, as did so much else, on Sept. 11.

Phase One lasted from Henry Kissinger's groundbreaking trip to Beijing in August 1971 until the massacre in Tiananmen Square on the night of June 3-4, 1989. During those 18 years the connection, based primarily on a common concern with the Soviet threat, moved steadily forward, even overcoming a difficult period in 1981-82 when the Reagan administration flirted with changing the very basis of the relationship with Beijing by upgrading relations with Taiwan.

But then came not only Tiananmen Square but also the end of the Cold War. This was Phase Two; it lasted from 1989 until Sept. 11, and it became increasingly rocky. The era of strategic convergence gave way to growing friction over trade, democracy and human rights, Taiwan, Tibet, religious freedom and more. And with the arrival of the new Bush administration, things seemed at first to get only worse.

When Gov. Bush called China a "strategic competitor" during the campaign (in contrast to the Clinton-Gore phrase "strategic partner"), Beijing looked the other way. But the Chinese were puzzled and angry that the unfriendly rhetoric, as well as a renewed commitment to a missile defense project that they regard as hostile, continued after Jan. 20; they had expected more continuity from a president whose father had served as ambassador in Beijing (famously bicycling around the city with Barbara) and whose advisers included such friends of China as Kissinger, Brent Scowcroft and George Schultz.

Beijing appeared, moreover, oblivious to its own contributions to the growing rift; its initial mishandling of the crew of the American military plane brought down by a reckless Chinese pilot; its treatment of dissidents, including American scholars of Chinese background; the increasingly aggressive (and often corrupt) business tactics in some of its provinces.

But with Sept. 11 the two countries have a common strategic adversary again, this time not Moscow but terrorism and extreme Islamic fundamentalism -- both issues that deeply concern the Chinese leadership, which has faced some groups inside western China with ties to al Qaeda. President Bush's meetings with Chinese President Jiang Zemin during the Asia-Pacific Economic Cooperation summit in Shanghai in November effectively set the stage for a new relationship -- Phase Three.

The problems listed above still exist, but it is not only possible, it is essential to use the opportunity to build again on what we have in common, while addressing openly what divides us. But how? Three critically important communiques were forged during the first phase of the relationship -- the Shanghai Communique (1972), the Joint Communique on Normalization of Relations (1978) and the Communique on Arms Sales to Taiwan (1982) -- the last of which settled the 1981-82 problem. While largely ignored or forgotten in the United States, these three documents are repeatedly invoked with near-religious significance by Chinese officials, as forming still today the basis of the relationship.

But the most recent of the three communiques is more than 19 years old. An enormous amount has happened since then -- the end of the Cold War, the emergence of Taiwan as a democracy, Tiananmen Square, Hong Kong's return to Beijing, the entry of China into the world trading system, new tensions and crackdowns in Tibet and more. These events have created new circumstances not envisioned by the drafters of the three original communiques.

It is time for Washington and Beijing to negotiate a fourth communique, one that would address these new issues and update the relationship based on a new realism. Negotiating a fourth communique will present some obvious difficulties, although none as great as those that faced the drafters of the first two. At home, there will be voices calling for changes in the old formula on Taiwan -- something that, I believe, would be possible on the margins but not on the core issue of independence. The United States would also need to insist on references to American views on religious and political freedom, human rights and Tibet, all of which Beijing maintains are domestic issues. (None was addressed in the original communiques.) To deal with our differences, the brilliant "our side-your side" formula in the original Shanghai Communique -- in which on areas of disagreement each side stated its own position -- should be the model.

On issues where our goals converge, such as terrorism, the Korean peninsula, narcotics, AIDS and the environment, a new communique could open new areas of cooperation. On terrorism, greater information-sharing and law enforcement cooperation on the activities of extremist Muslim groups (although both pose tricky issues if the United States is not to be turned into assisting undemocratic practices inside China) can be strengthened in specific ways that would contribute to our own national security, although the United States should not be lured into assisting undemocratic practices or anti-Tibetan actions inside China.

Diplomats are notoriously averse to rocking the boat, and many will say that the risks in such a difficult and politically delicate negotiation outweigh the rewards -- that we should, in a favorite State Department phrase, "let sleeping dogs lie."

I do not agree. The relationship with China, despite many ties, is not inherently stable; too many things lie beneath the surface that could disrupt it. We should not ignore the unique opportunity offered by the fact that China and the United States once again share a common strategic concern -- terrorism -- on which a revitalized relationship can be based.

A new communique might not be sufficient to prevent a future confrontation -- it could explode over events in Tibet or Taiwan in any case -- but it would go a long way toward building a stronger relationship with China and would perhaps help Taiwan open a more productive dialogue with the mainland. A new communique would also strengthen America's hand in promoting our own values and national agenda, combat terrorism and help stabilize a turbulent part of the globe at a time when China's importance in the world is increasing.

The writer, a former ambassador to the United Nations, oversaw negotiation of the 1978 Joint Communique on Normalization with China as an assistant secretary of state in the Carter administration.