The two allies are expected to seal an agreement on the relocation of a controversial US air base on the southern island of Okinawa at Saturday's security talks involving foreign and defence ministers.
The deal is set to move the base to existing land at the US Marine Corps's Camp Schwab on the southern island of Okinawa by building a new runway.
Although residents complain about aircraft noise there are also concerns about the environmental impact of the proposed relocation.
There had been suggestions the so-called "two-plus-two" meeting, which aims to promote bilateral defence co-operation, might be called off if the two sides did not reach a deal on the air base after years of disagreement.
But officials said this week that a deal had been reached after three days of fresh talks here, clearing the way for the meeting, at which an interim report is expected to be published on the realignment of US troops in Japan.
"Although media tend to focus on the relocation of the air base and cutting the number of (US) troops, there is another important issue in the talks - to strengthen the extent of co-operation between US troops and Japan's Self-Defence Force," said Satoshi Morimoto, a professor specialising in security issues at Takushoku University in Tokyo.
He said the real objective of the US was to cajole Japan into playing "a role of normal military troops", rather than continuing to limit its activity to within the strictest definition of "self-defence".
Japanese troops are barred by the pacifist 1947 constitution from using force except in the strictest definition of self-defence.
On the eve of the talks, Japan said that it had agreed to host a US nuclear-powered aircraft carrier in 2008 for the first time to help maintain security in the Far East, prompting strong protests here.
A spokesman for Japan's Defence Agency said the two sides had also already agreed at senior levels to share information and co-operation in some aspects of ballistic missile defence systems. Japan has already agreed with Washington to work on a next-generation joint missile defence system here after North Korea stunned the world in 1998 by firing a missile over the Japanese mainland into the Pacific.
The ongoing talks follow an agreement in February between Tokyo and Washington to seek greater co-operation between their troops and a reduction of burdens imposed on host communities such as noise, accidents and pollution.
Japan is the top US ally in East Asia and has sent troops to Iraq on the first mission since World War II to a country where fighting is ongoing. But polls show a majority of Japanese oppose extending the mission past December.
Japan also aims to reduce the number of US troops stationed in Okinawa, which accounts for less than one percent of Japan's land mass but remains the base for some 60 percent of the 38,340 US troops in the country.
Japanese Foreign Minister Nobutaka Machimura told reporters the reduction of US troop numbers "will be in the thousands," out of some 11,800 Marine Corps personnel in based in Okinawa. Japanese media reports that the troops will be moved to Guam, a US territory home to one of the most strategically important US bases in the Pacific.