TOKYO — Japan's embattled premier Tuesday abandoned a plan to move an unpopular US airbase entirely off Okinawa island, backtracking on a key election pledge after months of dithering that angered Washington.

"I really feel sorry as I visit here today that I must ask for the Okinawan people's understanding that part of the base operations would have to stay" on Okinawa, Yukio Hatoyama told reporters after meeting the local governor.

Hatoyama made the comment after being greeted by protesters on his first visit to the subtropical island since he took office in September vowing to ease the burden for the reluctant hosts of tens of thousands of US troops.

The row, which has centred on the planned relocation of the US Marine Corps Air Station Futenma, has cost the centre-left leader much domestic support and badly strained ties with Japan's key defence ally the United States.

Previous governments in Tokyo and Washington agreed in 2006 to move Futenma from a crowded urban location of Okinawa to a quieter coastal area, but Hatoyama promised to review the plan and move the base off Okinawa altogether.

However, a search for alternative sites in Japan has been met by more protests, leaving Hatoyama with few promising options ahead of a self-imposed May 31 deadline to resolve the matter.

Under the latest compromise plan -- not formally announced by the government but widely reported in domestic media -- Japan is proposing to stick with the original plan, with some modifications.

Futenma would now be moved, as originally agreed, to the coastal Henoko area of Nago city near the US base of Camp Schwab, but its runways would be built on stilts rather than landfill to help protect coral reefs.

About 1,000 US Marines and their helicopter operations would be moved to the remote island of Tokunoshima, 200 kilometres (120 miles) northeast of Okinawa, although the plan has been met by protests on that island too.

The United States, whose envoys were discussing the issue with Japanese senior officials in Tokyo on Tuesday, is reportedly unhappy with a plan to split up Futenma's Marine forces as operationally difficult.

Hatoyama -- whose approval ratings have dived into the 20 percent band amid the row ahead of upper house polls due in July -- was meeting officials in Okinawa in a bid to sell the compromise plan.

"We have faced the reality that it would be difficult to remove all the operations out of Okinawa prefecture," Hatoyama said during his meeting with governor Hirokazu Nakaima. "We need to ask for the understanding of Okinawa's people for bearing some of the burden."

He also told Nakaima: "Initially, there was an argument to move it overseas. But when we consider the Japan-US alliance and matters related to neighbouring nations, it is difficult to do so from the viewpoint of deterrence. It is impossible in reality.

"Therefore we have tried to find a way to move it outside of the prefecture but have faced the reality that it would be difficult to move it out altogether."

The issue has stirred strong passions on Okinawa, site of some of World War II's bloodiest battles, and still the host of more than half of the 47,000 US troops stationed in Japan under a post-war security treaty.

When Hatoyama arrived for his one-day trip to the island, about 400 protesters gathered before the Okinawa government building with flags and banners reading: "Never accept a new base in Henoko!"

Hatoyama's visit to Okinawa followed a mass rally late last month, which attracted 90,000 people opposed to the 2006 deal, which the United States has insisted is the best option to ensure Japan's security.

Hatoyama was also due to meet the anti-base mayor of Nago, Susumu Inamine, and visit both the Futenma base in Ginowan and Camp Schwab. Later this week he is due to meet three mayors from Tokunoshima island.

More Okinawan residents were preparing to protest near Camp Schwab.

"We don't even know what Prime Minister Hatoyama is visiting here for," protest organiser Hiroshi Ashitomi told AFP. "We will convey our message that local residents don't want any more bases on Okinawa."

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