WASHINGTON -- Two Japan experts in the U.S. administration will leave their office, raising concern about the impact on efforts to resolve a host of bilateral issues. Kurt Campbell will quit as deputy assistant secretary of defense and join the Center for Strategic and International Studies, a U.S. think tank, on May 1, while Rust Deming, deputy assistant secretary of state, will become ambassador to Tunisia. Campbell worked for the Treasury Department and the National Security Council before assuming his present post in May 1995. His achievements included the updating of the U.S.-Japan defense cooperation guidelines. Deming, who previously worked at the U.S. Embassy in Tokyo, is responsible for bilateral security and trade relations. The departure of Campbell and Deming, coming in the final year of the administration of President Bill Clinton, could be a drag on progress in talks with Japan on the U.S. military presence in Okinawa and Tokyo's host-nation support for U.S. bases in Japan, a U.S. official said. Campbell played a central role in the bilateral talks on relocating the U.S. Marine Corps heliport now at the Futenma Air Station in Ginowan, central Okinawa -- a key part of the 1996 Japan-U.S. agreement for reorganizing the Okinawa bases. A Japanese diplomat in Washington described Campbell as "one of the few senior U.S. officials who understand the importance of the Okinawa issue," adding that Tokyo was relying on him for the final settlement to the Futenma relocation. Once the two depart for their new jobs, it will become difficult for the two governments to reach a final settlement on the Futenma issue before a new U.S. administration is established next year, said a U.S. official in Washington.