Many in Tokyo and Washington will be keeping a close eye on a mayoral election Sunday in Okinawa that is likely to affect a matter of long-standing concern between the two governments.

In the Nago mayoral race, incumbent Tateo Kishimoto, 58, is being challenged by 42-year-old Yasuhiro Miyagi, a former Nago assemblyman who opposes the planned construction of a joint civilian-U.S. military airport off the city's coast.

"All our efforts over the years (regarding the proposal) would come to nothing should Mr. Kishimoto lose," an official at the Defense Facilities Administration Agency in Tokyo said.

Pre-election speculation indicates that Kishimoto is leading the race. But local journalists said Miyagi might stand a chance if the mayor's supporters feel so secure of their candidate's victory that they do not bother to vote.

Mitsuo Matayoshi, 57, from a minor political party, also announced his candidacy, but the election is widely seen as a two-man race.

Japan and the United States agreed in 1996 on the construction of an offshore facility to be used by the U.S. Marine Corps as a condition for returning the Futenma Air Station, which is in a densely populated area in the city of Ginowan.

Despite Okinawans' desire to be free of the U.S. military after the ground battles of World War II and decades of U.S. rule, the local economy has had to depend on the bases, especially in rural northern areas such as Nago.

Nevertheless, in a plebiscite held in December 1997, 53 percent of voters opposed construction of a new facility, compared with 45 percent who supported it, with many hoping the central government would offer more economic promotion measures.

Although Nago's population is concentrated along another stretch of coast and would not be directly affected by construction of the facility, Sunday's election will be the first time in four years that local voters will have their opinions heard.

Kishimoto, who was elected soon after the 1997 plebiscite, avoided discussion on the issue during that election campaign.

But this time, he reached agreement with the central government in December on constructing the site on a reef off the city's Henoko district, although he avoided going into details, such as the size of the facility and the construction method to be used.

The Kishimoto camp, as well as central government officials, hope his victory will add momentum to the plan, which under the initial scheme should have been finished by now.

The central government has attempted to push the plan forward using various means, including holding the Group of Eight summit in Nago in 2000 and promising special budgetary allocations totaling 100 billion yen in 10 years for northern Okinawa.

Last week, just before the election campaign kicked off, the government approved a package of bills to bolster Okinawa's economy, including special tax measures for the financial, information and communications industries.

As another indication of the central government's commitment to the new facility, New Komeito, a member of the tripartite ruling coalition, is backing Kishimoto this time, after supporting a rival candidate in the previous mayoral election.

The proposed construction has changed greatly from the plan at the time of the 1997 plebiscite.

The planned facility has been enlarged to a joint-use civilian-military airport with a 2,000-meter runway from a 1,500-meter-long movable heliport in line with proposals from the prefectural and municipal governments to develop the northern area of Okinawa Island.

However, critics say that many local residents question the need for such an airport in an area within an hour's drive of Naha International Airport.

Even some local leaders in favor of the plan are opposing any method of construction that would increase noise pollution and further damage the marine environment.

A Defense Facilities Administration Agency study last year confirmed that at least five dugongs inhabit the waters near the proposed site. Miyagi has led activities to protect the endangered mammals, which are believed to live nowhere else in Japan.

The government has set aside a budget of 150 million yen for dugong research and protection and promised to pay the utmost consideration to the environment during construction of the airport. But opponents say they still fear adverse effects on the flora and fauna.

Another headache for the incumbent mayor is the demand by Okinawa Gov. Keiichi Inamine that the U.S. forces' use of the airport be limited to 15 years, a condition for the construction going ahead.

Although Tokyo has officially said it will continue to convey the demand to Washington, U.S. officials have repeatedly rejected the idea, and former Foreign Minister Makiko Tanaka said during a visit to Okinawa earlier this year that that condition is unfeasible.