YOKOSUKA NAVAL BASE, Japan — Japan has conditionally agreed to build 800 additional residential units near Yokosuka Naval Base to replace servicemember housing lost when four Yokohama-area U.S. Navy bases are returned to Japanese control.

U.S. officials said Monday the deal — which would be the second largest land return in 30 years — is conditional on Japan building new housing units for servicemembers and dependents who would be uprooted by base closings.

Japan has agreed to build the new housing as close to Yokosuka as possible.

The deal still will leave the area several hundred housing units short, officials have said.

Although a timetable has yet to be established, the completion of previous Yokosuka-area housing projects has taken years.

Under the proposed transaction, more than 700 acres containing American housing areas, communications facilities and warehouses would be returned to Japanese control.

All of the Fukaya Communications Site, Tomioka Storage Area and Negishi Dependent Housing Area and most of the Kamiseya Communications Station will be turned over to the Japanese at a date to be determined later, a U.S. Forces Japan spokesman said.

From the outset of negotiations, American officials insisted an agreement for new housing was needed before “the United States government can consider release of those facilities and areas when they become no longer needed,” USFJ spokesman Air Force Col. Victor Warzinski said.

Initial plans recommend new housing be built at the Ikego Heights housing area, which already has approximately 850 units, about 10 miles from the main Yokosuka base.

Navy housing is at a premium in Japan.

According to USFJ, about 3,000 American families or servicemembers in Kanagawa Prefecture live in private, off-base housing.

The number of families hoping to live in Navy housing plus military personnel who cannot live with their families due to the housing shortage indicates “a total of a thousand and some hundreds of housing units are needed,” Warzinski said.

Navy officials referred questions about the housing issue to USFJ, but acknowledged it is a major concern.

“At any given time, the U.S. Navy has under consideration numerous plans concerning the best use of bases and facilities worldwide,” said Jon Nylander, a U.S. Naval Forces Japan spokesman.

“Ensuring adequate housing is provided for our sailors and their family members wherever they may be assigned is one of the Navy’s top priorities.”

A spokesman for the Japan Defense Facilities Administration Agency, which controls issues related to U.S. bases, said the agreement was reached late last week.

The Japanese government first broached the specific proposal at a February meeting of the American and Japanese joint committee, he said.

Agency spokesman Masaru Muraoka said the return’s timing and the former bases’ eventual fate will be decided later.

“The government of Japan desires prompt release [of the land] in consideration of the repeated requests from the local governments and residents, and that the understanding of local governments is necessary for the housing construction,” a statement released by a joint committee said.

A senior Yokohama City official, while welcoming the return of the four facilities, told Asahi Shimbun newspaper the city would “deal cautiously” with the new housing projects.

If the conditions are met, the land transfer would be the largest on mainland Japan since the 1970s, when parts of U.S. Air Force facilities near Yokota Air Base were returned.

Chiyomi Sumida contributed to this report.