Words matter, in diplomacy and in law.

Last week President Bush was asked if the United States had an obligation to defend Taiwan if it was attacked by China. He replied, "Yes, we do, and the Chinese must understand that. Yes, I would."

The interviewer asked, "With the full force of the American military?"

President Bush replied, "Whatever it took" to help Taiwan defend itself.

A few hours later, the president appeared to back off this startling new commitment, stressing that he would continue to abide by the "one China" policy followed by each of the past five administrations.

Where once the United States had a policy of "strategic ambiguity" -- under which we reserved the right to use force to defend Taiwan but kept mum about the circumstances in which we might, or might not, intervene in a war across the Taiwan Strait -- we now appear to have a policy of ambiguous strategic ambiguity. It is not an improvement.

The United States has a vital interest in helping Taiwan sustain its vibrant democracy. I remain as committed today to preserving Taiwan's autonomy as I was 22 years ago when I cast my vote in favor of the Taiwan Relations Act, which obligates the United States to provide Taiwan "with such defense articles and defense services . . . as may be necessary to enable Taiwan to maintain a sufficient self-defense capability." I remain committed to the principle that Taiwan's future must be determined only by peaceful means, consistent with the wishes of the people of Taiwan.

What is the appropriate role for the United States? The president's national security adviser last Wednesday claimed that "the Taiwan Relations Act makes very clear that the U.S. has an obligation that Taiwan's peaceful way of life is not upset by force."

No. Not exactly. The United States has not been obligated to defend Taiwan since we abrogated the 1954 Mutual Defense Treaty signed by President Eisenhower and ratified by the Senate. The Taiwan Relations Act articulates, as a matter of policy, that any attempt to determine the future of Taiwan by other than peaceful means would constitute "a threat to the peace and security of the Western Pacific area" and would be, "of grave concern to the United States."

The act obliges the president to notify Congress in the event of any threat to the security of Taiwan, and stipulates that the president and Congress shall determine, in accordance with constitutional processes, an appropriate response by the United States.

So, if the choice is between an "obligation" and a "policy," what is all the fuss about?

As a matter of diplomacy, there is a huge difference between reserving the right to use force and obligating ourselves, a priori, to come to the defense of Taiwan. The president should not cede to Taiwan, much less to China, the ability automatically to draw us into a war across the Taiwan Strait. Moreover, to make good on the president's pledge, we would almost certainly want to use our bases on Okinawa, Japan.

But there is no evidence the president has consulted with Japan about an explicit and significant expansion of the terms of reference for the U.S.-Japan Security Alliance. Although the alliance provides for joint operations in the areas surrounding Japan, the inclusion of Taiwan within that scope is an issue of the greatest sensitivity in Tokyo. Successive Japanese governments have avoided being pinned down on the issue, for fear of fracturing the alliance.

As a matter of law, obligations and policies are also worlds apart. The president has broad policymaking authority in the realm of foreign policy, but his powers as commander in chief are not absolute. Under the Constitution, as well as the provisions of the Taiwan Relations Act, the commitment of U.S. forces to the defense of Taiwan is a matter the president should bring to the American people and Congress.

I was quick to praise the president's deft handling of the dispute with China over the fate of the downed U.S. surveillance aircraft.

But in this case, his inattention to detail has damaged U.S. credibility with our allies and sown confusion throughout the Pacific Rim.

Words matter.

The writer, a U.S. senator from Delaware, is the senior Democrat on the Senate Foreign Relations Committee.