When foreign investors buy Washington real estate, secrecy is often the essence of a deal.

Foreigners -- chiefly Japanese and British investors -- now own at least 40 downtown office buildings, about one-third of the office space in the central business district. Some of the deals have been widely publicized, but others have been shrouded in secrecy worthy of a military mission behind enemy lines.

The Justice Department has a new landlord at the Judiciary Center building at 555 4th St. NW, although few lawyers who work there, including U.S. Attorney Joseph E. diGenova, are likely aware of the new owner -- a Japanese textile firm. The 350,000-square-foot, 11-story beige concrete and glass office building, located a short distance from both the federal and D.C. courthouses, was built in 1983 by Rozansky and Kay Construction Co. at a cost of $51 million. But the building was ahead of its time. Alan I. Kay, one of the developers, said that "at the time there was too much space available" in the courthouse vicinity and the building was never leased.

Kay said he opted for a $4 million profit, rather than $8 million a year in carrying costs, and sold the unleased building in 1984 for $55 million to General Electric Credit Corp., which sold it to the Dallas-based Hall Real Estate Group in May 1986 for $76 million.

But now the real estate syndication group headed by Craig Hall has also unloaded the property -- fully leased through 1995 to the federal government -- to a group that is simply called 555 Fourth Street Associates.

The general partnership bought the property in April for $86.5 million, and while the Hall syndicate announced the sale in a press release, it refused to answer any questions about the actual owners. "The buyer has been determined to keep his name quiet," one Hall official said.

Local real estate sources, however, have identified the owner as Kondo Boseki, a Japanese textile firm.

Such secrecy is not uncommon among some foreign buyers, who have often written secrecy provisions into their purchase contracts forbidding their American sellers to disclose the buyer's name, even if it is secret during the negotiations and the buyer later learns the identity.

"There's an inculcated distaste for flash," said Russell C. (Rusty) Lindner, a managing partner of a Washington real estate investment firm who wrote his master's thesis at the Massachusetts Institute of Technology on Japanese real estate investment in the United States. "They really don't promote themselves. They're worried about backlash" from Americans worried about extensive foreign purchases of key U.S. properties.

In fact, when Americans have been offered enough money, secrecy on their part has been no problem. Nor, when a quick deal was of paramount importance, has the issue of speed been a problem for the foreign investors.

Typically, foreign investors have taken months, even a year or more, to complete a deal by the time the executives in the home office across the Atlantic or Pacific ocean have been consulted. But foreign investors have moved swiftly when American building owners have imposed deadlines to sell their properties, such as late last year when many owners wanted to sell by Dec. 31 to beat higher capital gains taxes that took effect New Year's Day.

One such quick Japanese acquisition -- the nine-story Esplanade Building at 1990 K St. NW -- was completed in 23 days last December, a speed Lindner said is "often used as an example of how quickly the Japanese can move."

Even now, the developer who sold the office and retail property with its brown paneled facade said he is not sure who bought it.

The developer, who himself requested anonymity, said that "we were approached by Cushman & Wakefield {commercial realty agents} representing undisclosed Japanese interests."

When it came to the final negotiations, the D.C. developer recalled, "I said I wouldn't consider anything less than $55 million. They offered $3 million less. I knew they'd be back within an hour and they were" -- with the full $55 million offer.

"They paid all cash," the developer said of Mitsubishi Trust and Banking Corp., which represented the Japanese buyers. "I guarantee they paid full market price, but they didn't overreach.

"They wanted to buy before the end of the year and I wanted to sell to avoid the higher capital gains tax. That's why it happened.

"To this day I don't know who bought it," he said. "All I wanted was the cash. Once I found they were going to wire money to my bank, I lost interest in who they were. We had a written pledge of anonymity if we accidentally found out who bought it."

The deal was closed on Dec. 30, just in time for the D.C. developer to catch a flight to Florida to join his wife for a New Year's Eve celebration.