United States and Japanese officials have cut a deal that will shift 9000 US marines from the southern Japanese island of Okinawa to Guam and other Asia-Pacific sites.
A joint US-Japanese statement says 5000 will go to Guam and the rest to other sites such as Hawaii and Australia.
About 10,000 will remain, the BBC reports.
The statement says the updated version of a 2006 plan is needed to achieve "a US force posture in the Asia-Pacific region that is more geographically distributed, operationally resilient and politically sustainable".
It will help the allies work around a dispute over moving the Futenma air base from a crowded part of Okinawa to a new site.
Locals say having the Futenma base near a city is dangerous and noisy and they want it removed from the island altogether.
Occasional well-publicised instances of bad behaviour and criminality by US personnel, including a 1995 rape of a 12-year-old girl by three US servicemen, have fuelled the concerns.
At the end of World War II, American occupation forces took control of Okinawa, after 100,000 Japanese died in the Battle of Okinawa.
In modern times, under a 1960 bilateral security treaty, there have been about 47,000 American troops in Japan.
The revised agreement comes ahead of a visit to Washington by Japanese Prime Minister Yoshihiko Noda.
Japan has been unable to fulfil the conditions of an agreement over Okinawa signed in 2006 under which it had to find an alternative location for the Futenma air base before US troops were redeployed.
Proposed alternatives met heavy local opposition. At the beginning of talks this year, both countries said they had agreed to de-link the two issues.
In the latest statement, they said they still agreed that Futenma should be relocated to Camp Schwab, in a sparsely populated area miles north of Naha, in line with the 2006 deal.
This "remains the only viable solution that has been identified to date", the two governments said.
The issue has put a strain on the US-Japan security alliance, which both countries see as critical to maintaining the balance of power in Asia as China rises, says our correspondent.
Former Prime Minister Yukio Hatoyama promised to shift the base off the island, but he resigned in 2010 when he failed to get agreement on another location.
It remains unclear when the troops will be redeployed and when the Futenma base will be moved.
US Defence Secretary Leon Panetta said the US would now work with the Japanese Self Defense Force to ''implement these decisions''.
"Japan is not just a close ally, but also a close friend,'' he said. ''And I look forward to deepening that friendship and strengthening our partnership as, together, we address security challenges in the region."
The latest announcement is intended to take the sting out of the dispute before Mr Noda visits Washington next week, says the BBC's Roland Buerk in Tokyo.