At 11 p.m. last Thursday night, a group of American reporters met in the Okura Hotel's Orchid Lounge with what they were told to identify, improbably, as "sources close to U.S. trade officials."

The message sounded ominous: Talks with the Japanese about limiting auto exports were going badly, the sources confided. Japan's offer was unsatisfactory, not nearly enough to fend off a congressional quota bill that would be even tougher on Japanese auto makers. More proposals, it was hoped, would be forthcoming from the Japanese side.

About the time this gloomy assessment was appearing in the U.S. press 12 hours later, sources close to the same U.S. trade officials were singing a different song. Japan had changed its proposal, although modestly, overnight and everything looked "upbeat." William Brock, the U.S. trade official to whom all those mysterious sources were so close, surfaced publicly to say that the great auto dispute was settled and the prospects of a congressional quota bill were dead.

Bewildered reporters later concluded that they had been gulled in an American scheme to put overnight pressure on the Japanese.

"I can still feel the hook in my throat," said one reporter who had happily swallowed the bait the night before.

The episode was a fitting ending to the auto export story that had more than its share of self-serving news leaks, trial balloons and downright deceptions on both sides of the Pacific Ocean. To an unusual extent, the bargaining over export restraint was conducted in the news columns and air waves.

Signals went up in Tokyo to achieve a desired effect in Washington, and vice versa. Trial balloons were floated in Tokyo by one ministry to signal something to another ministry or to the auto industry.

On March 18, the Reagan administration tried to claim victory on the basis of an inflated Tokyo news report that the Japanese industry was caving in. Tokyo tested the limits of U.S. seriousness by surfacing, through anonymous sources, a bewildering series of numbers suggesting how far it was willing to bend.

Some parts of all this stemmed from official tactics and other parts from reporters' eagerness to claim discovery of a hot new development in a long and competitive running story.

But the official news leakage may have reached new heights in the auto case because of one unusual fact: It was a story of negotiations with only one acknowledged negotiator -- the Japanese Ministry of International Trade and Industry (MITI). The Reagan administration, trying to keep its free-trade skirts clean, maintained throughout that it was not a party to any attempts to restrict Japanese exports.

That placed Japan in a difficult position. Midway through the affair, a U.S. official observed that it would be much easier for Japan to give in and restrict exports if the White House could give a clear signal of what it wanted, which it could not. The result, he observed, was the series of hazy news leaks and trial balloons.

"The Japanese can't reach a consensus on this one and what you're seeing is the smoke signals of them trying to reach one," the official added.

One highly publicized leak apparently stemmed from Japan's desire to show that, in fact, the White House was in the bargaining ball game. Stories surfaced in Washington and Tokyo that Ambassador Mike Mansfield had transmitted a Reagan target for limiting exports to 1.6 million cars.

Mansfield denied it. The Japanese Foreign Ministry denied it. MITI said it was true -- and still says it was true. The reporters and readers can take their chance.

Bargaining without a visible bargaining partner, the Japanese floated a baffling series of bargaining points. Auto industry reporters here were told the big auto makers might sue if the government forced them to buckle under. Reporters covering MITI were told 1.7 million exports this year was the bottom line, one of the leaks that turned out to be approximately true.

At the point, MITI and the Foreign Ministry were pedding conflicting news leaks to protect their bureaucratic turfs. Readers would be told by "government sources" one day that the Foreign Ministry would negotiate the dispute and that the Foreign Ministry did not think Japan should cave in quickly. The next day, readers would learn -- also from "government sources" -- that MITI was in command and felt concessions should be offered quickly.

Trial balloons are floated daily by anonymous spokesmen in Washington, Tokyo and every other world capital, but they are especially easy to cast aloft here. Each ministry and industry has its own coterie of reporters who obligingly report verbatim, and with minimal skepticism, almost everything their sources tell them.

Moreover, the Japanese press clubs are notoriously protective of their own turfs and with few exceptions foreign reporters are barred from the daily briefings. The foreigners usually spend the day trying to figure out which of the morning's conflicting news leaks are true and which merely represent what a ministry wants to put out.

On the day that every major Japanese newspaper proclaimed the MITI decision to limit exports to 1.7 million cars this year, a MITI official directly involved categorically denied it.

"It is purely the work of their [the reporters'] imagination," the official said.

Tokyo's daily assortment of confusing, conflicting leaks may be responsible for the fact that the Japanese press inspires as little confidence in its readers as does the U.S. press. Last year, the Japan Newspaper Publishers and Editors Association conducted its annual survey to determine its confidence rating.

"Can you trust what you read in the newspapers?" It asked a sample of 1,569 men and women.

Only 11 percent replied, "definitely, yes.