ASUMMIT MEETING between President Obama and Japanese Prime Minister Yoshihiko Noda of Japan attracted virtually no attention in Washington on Monday — which in itself said something about the relative decline of a once-vital alliance. But lost in questions about North Korea and China at a White House press conference was a small but significant diplomatic breakthrough: the easing of the two-year-old standoff over U.S. bases on the Japanese island of Okinawa. At a minimum, the bargain prevented the U.S.-Japanese summit from making negative headlines. At best it may open the way for an invigoration of strategic cooperation at just the right time in East Asia.

A joint statement issued by the two countries before Mr. Noda’s visit said the United States would move forward with plans to redeploy 9,000 Marines from Okinawa to Guam and several other Pacific bases — a step that could ease tensions on Okinawa, whose residents have been demanding the reduction or closure of U.S. installations. The agreement delinked the redeployment from a controversial and costly plan to create a new air base for the Marines at another Okinawa site. This could allow the Japanese government to move forward with the base as political conditions allow — or open the way for an alternative plan. While it doesn’t solve the Okinawa basing problem, officials said the agreement would unstick U.S.-Japanese strategic cooperation and allow other initiatives to progress, including new plans for joint training.

For both sides, the compromise reflected a political maturation. Mr. Noda’s Democratic Party of Japan came to power in 2009 promising to shake up U.S.-Japanese relations and reopen a 2006 agreement on the Okinawa bases. It then missed its own deadline for offering an alternative. Mr. Obama and his first defense secretary, Robert M. Gates, reacted with public displays of impatience and irritation; their rough treatment of then-Prime Minister Yukio Hatoyama helped bring about the collapse of his government. The result was a counterproductive distraction in security relations at a time when Japan and the United States ought to be jointly focused on issues such as the North Korean nuclear threat and China’s expanding regional ambitions.

The agreement could unravel. Three members of the Senate Armed Services Committee — James Webb (D-Va.), John McCain (R-Ariz.) and Chairman Carl Levin (D-Mich.) — have questioned the lack of detailed cost estimates and planning for the deployment of some 5,000 of the Marines on Guam. Mr. Webb argues that the plan for the Okinawa base is not feasible. At his impetus, Congress mandated an independent study of U.S. deployments in East Asia that has yet to be completed. The deal nevertheless is a welcome step toward removing a major irritant in U.S.-Japanese relations, and strengthening an alliance that both countries need more than ever.