A U.S.-Japan agreement to build a heliport at an American military base on Okinawa (search) ran into opposition from the island's residents Thursday, and Japan's defense chief predicted Tokyo would struggle to get their approval for the plan.

The deal struck Wednesday would close the Marine Corps Air Station, Futenma, and build a new heliport at another base on the island, Camp Schwab.

Critics of the U.S. bases support closing Futenma — but also oppose any new military construction.

Defense Agency chief Yoshinori Ono told a parliament committee Thursday that he anticipated difficult negotiations after discussing the plan with Okinawa Gov. Keiichi Inamine.

"The governor's reaction was tough, but I asked for his understanding and cooperation on the issues of reducing the number of Marines and integrating bases," Ono told committee members. "I understand it will be tough."

On Okinawa, about 40 members of civic groups opposed to the plan met with Inamine to voice their grievances.

"The governor should clearly reject the new base which Japan and the U.S. agreed on," activist Tokunobu Yamauchi told reporters.

Kyodo News agency quoted Inamine telling reporters Thursday that the plan is "completely incompatible" with his government's call to move Futenma off Okinawa.

The U.S. considers Okinawa the linchpin of its military posture in East Asia. The island hosts most of the 50,000 troops based in Japan.

However, Okinawans have long complained of crime, crowding and noise associated with the bases, and Japan has pushed for adjustments in the U.S. presence.

Wednesday's agreement, which scuttled a much-protested plan to build a heliport on a coral reef off Okinawa, paved the way for broader talks on the realignment of U.S. forces in Japan.

U.S. Secretary of State Condoleezza Rice (search) and Defense Secretary Donald Rumsfeld (search) are to meet their Japanese counterparts on Saturday in Washington.

American officials have not released any changes being considered, but Japanese Foreign Minister Nobutaka Machimura said Wednesday they would involve reducing the number of the thousands of Marines on Okinawa.

Machimura gave no details. However, Japanese news reports said about 4,000 Marines would be moved to other bases in Japan and on the U.S. Pacific island territory of Guam.