The case of Richard V. Allen is a mystery with more false clues than "Murder on the Orient Express."

Did the national security adviser "accept" $1,000 from a party of three Japanese journalists the day after the inauguration? Or was it $10,000? Was the lacquer stationery box presented to Nancy Reagan worth $75, or was it worth $273? And was she interviewed for five minutes, or was it 15 or 20?

And what about the watches? Allen "accepted" a gold Seiko from his Japanese visitors before Inauguration Day and a silver one after. Apparently, he couldn't decide between them, and it's not important except that before he was sworn in, it was okay, and afterward, it became a federal case.

All of the information in the case is as perishable as the Japanese cherry blossoms we so briefly enjoy in the spring.

The ordinary newspaper reader has learned little about this baffling matter from the administration. Press spokesmen take pious refuge in "no comment" because the "matter is under investigation." But others in the White House, beginning with the president, act like lawyers for the defense. It is improper, they say, to vouchsafe anything but exoneration.

The president told us almost immediately that "there was no evidence of wrongdoing."

He was going on the word of White House counsel Fred Fielding, another old friend of Allen, who closed down the FBI investigation even as we were being told about it. "No law had been broken," Fielding said just hours before the FBI informed us that the probe was still in process.

Counselor Edwin Meese III, biggest of the White House Big Three, stepped forward to let us know that he had been assured by the FBI that everything was hunky-dory, even though we had been assured that he had not been in touch with the FBI.

If you are baffled by the case, not to worry. So is the FBI. The bureau has been on the job since mid-September.

Some unnamed White House official has given them a poor review. "The bureau did not do a very thorough job."

Did the FBI have its heart in it?

The most astounding fact to emerge since we first heard the confusing story of the generous Japanese--who told us one day that Allen solicited their gift and the next that they offered it--is not in dispute. It is that FBI Director William H. Webster called Allen during the course of the investigation.

The call, we are told by Webster's bosses in the Justice Department, was "unauthorized." They tell us further that Webster told the target of the investigation that he was off the hook, that the Japanese had backed him up on the story that they had left off only $1,000.

It was most thoughtful of Webster. But it suggests that the bureau may be slipping back to the days of L. Patrick Gray, an FBI director who, during the Watergate investigation, faithfully reported to his superiors in the White House.

For sure, anyone being followed would appreciate a soothing call from the chief of the G-men.

That leads us to the question of why the feds can't crack the case.

Have they lost the knack for the real thing, since running their manufactured crime wave in the Abscam case? That curious exercise was supposed to clear their name of the Watergate taint. They were bent on proving that the legislative branch of the government includes as many crooks as the executive branch.

They engaged a convicted con man, Melvin Weinberg, to set up a huge and expensive plot whereby members of Congress were lured to confabulations with a fake "sheik" who would bring vast riches to their home districts and cut them in on the take.

They were videotaped as they grabbed for the money.

Sen. Harrison A. Williams Jr. (D-N.J.), was one of their targets but was singularly uncooperative. For a solid year, he flatly refused money. Finally, in desperation, the undercover agents hounded him into expressing an interest in a titanium mine.

Like the other six members of Congress implicated in Abscam, Williams was tried and convicted. Legal authorities have expressed concern about "entrapment," about the propriety of inventing crimes when so many exist.

Williams is now facing expulsion from the Senate.

At no time has he received a sympathy call from the director of the FBI.

Why is Allen so different? Did Meese's query convey to Webster the feeling that the president would appreciate a lack of zeal?

We have no way of knowing. The director is a former federal judge, and he knows the rules about communing with the subject of an investigation.

Webster is on the spot now. He must explain to us why he felt obliged to give Allen a ring.

But he can't be expected to enlighten us as to why the president's men have been so solicitous about Allen, so cavalier about the "hound's tooth" standard for White House ethics.

Is he invaluable to the president in the White House? Or is it too dangerous to fire him? Someone else will have to answer those questions for us.