U.S. President Barack Obama has decided to abandon plans to deploy a missile defense system in Europe to counter an Iranian missile threat. The way it was carried out raises questions about U.S. commitments to its allies. The missile defense program is a partnership between Washington and its allies. As such, decisions regarding its future should be made together, not imposed by one on another.

Still, Mr. Obama's decision makes sense. It has removed the probably greatest barrier to the progress of negotiations between the United States and Russia for nuclear arms reductions. It is strongly hoped that the U.S. and Russia will make a great step forward to conclude their negotiations by yearend.

Concerned about the prospect of Iranian missiles attacking the U.S. and its European allies, former U.S. President George W. Bush developed a plan that would deploy a sophisticated radar system in the Czech Republic and 10 ground-based interceptors in Poland. That decision infuriated Russia, which insisted that the deployment threatened to neutralize its nuclear deterrent, a charge that the U.S. consistently denied. Equally important for Moscow but rarely stated outright was fear that the integration of the two countries more deeply into the U.S. defense system would undercut Russian influence in an area that it considers part of its sphere of influence.

Yet, on Sept. 16, Mr. Obama announced that he was scrapping the planned deployment and would instead use smaller missiles, first on ships, and then later on land, to counter the Iranian threat. As Mr. Obama explained, "President Bush was right that Iran's ballistic missile program poses a significant threat." Assessments of that threat have changed, however.

Now, the chief danger is seen as emanating from short- and medium-range missiles, rather than the long-range missiles for which the original deployments were best suited. It is also thought that moving the interceptors further south will offer more defense for Israel, another U.S. ally threatened by Iranian missiles. (More security for Israel would also dampen the enthusiasm in that country to launch a preemptive strike against Iran.)

Anticipating criticism, Mr. Obama noted: "This new approach will provide capabilities sooner, build on proven systems and offer greater defenses against the threat of missile attack than the 2007 European missile defense program."

For many observers, the real issue is not defense against Iranian missiles. Rather, this move is seen as part of the broader U.S. effort to reset relations with Russia, which the Obama administration has made a priority. Eliminating the missile defense irritant is a big step forward in that effort.

Ideally, Washington can now enlist Moscow to help halt the Iranian nuclear program, an effort for which Russia has thus farshown little enthusiasm. It could also lessen Russia's objections to strategic arms cuts. Russian leaders have responded to the move positively, applauding it as a "responsible approach" and for respecting their national concerns.

In his visit to Moscow in July, Mr. Obama and Russian President Dmitry Medvedev agreed to limit the number of strategic nuclear warheads to 1,500 to 1,675 and that of launchers to 500 to 1,100, under a new treaty to succeed START-1 (Strategic Arms Reduction Treaty-1), which expires in December. It is hoped that in a short time the world will be able to see a concrete payoff from Mr. Obama's move.

But while relations with Russia may improve, there is a distinct chill coming from Europe. The governments of Poland and the Czech Republic took considerable criticism from their publics for agreeing to the U.S. deployments in the first place. The governments are angry that they took that heat for nothing, and worry that their security is being traded for better relations between Washington and Moscow. As one counter to that criticism, the U.S. has agreed to deploy a significant number of smaller interceptors in Poland.

While U.S. officials say there was consultation with European allies, there appeared to be a scramble to reassure the two countries, both of which belong to NATO. In a late-night phone call to leaders of the two countries, Mr. Obama repeated the U.S. commitment to their defense and reaffirmed "our deep and close ties." The timing also suggests that the announcement of the decision on the European missile defense system may have been premature: It was made the day before the 70th anniversary of the Soviet invasion of Poland at the start of World War II.

In Asia, China worries that U.S. plans to deploy a missile shield in Asia — which Japan is joining — could undermine its nuclear deterrent. It may complain loudly to the U.S. Japan and the U.S. need to correctly assess the nature of the threats they face and consider the most appropriate way to deal with them. In doing so, they should pay utmost attention to minimizing friction and maximizing stability in the region.