Japan plans to return, at the request of Washington, plutonium provided by the United States for research purposes during the Cold War, government sources said Tuesday.
The government wants to be seen contributing to nuclear nonproliferation, the sources said.
The Obama administration asked for the plutonium back as part of a drive to strengthen nuclear security.
The two governments aim to work out the details by the third nuclear security summit, scheduled for March 24 and 25 in the Netherlands, the sources said.
At the summit, Prime Minister Shinzo Abe plans to cite the agreement as a specific measure taken by Japan to help nonproliferation, they said.
The plutonium is kept for use as nuclear fuel at the Japan Atomic Energy Agency's fast critical assembly in Tokai, Ibaraki Prefecture. The facility is designed to study characteristics of fast reactors.
Some of the plutonium, which totaled 331 kg at the end of 2012, was produced in Britain, according to the Cabinet Office.
While Tokyo has told Washington it will comply with the request, Japan wants the fuel be replaced with lower-grade plutonium to continue the research effort, the sources said.
The United States has been pressing Japan to return the plutonium since the first nuclear security summit was held in 2010, at the initiative of President Barack Obama. Japan initially resisted, citing the need to research fast reactors, the sources said.
The government has now decided that continued refusal could damage the relationship with the United States, they said.
It is also necessary to sweep away any concerns the international community may have about Japan's reluctance to part with the weapons-grade plutonium, one source said.