Near as I can tell, I'm alone with an official denial that, during a recent telephone conversation, Saudi Arabian King Fahd threatened President Reagan with withdrawal of $100 billion from American banks as a show of protest against Israel's siege of Beirut.

The threat was seen as bringing home Arab anger for the administration's presumed support of Israeli tactics and, then, as prompting a photo opportunity in which the president demonstrated his wrath over a subsequent telephone conversation with Prime Minister Begin.

The report appeared in Haynes Johnson's column Aug. 15. While attributing it to people who in the past have proved reliable, Mr. Johnson carefully noted an uncertainty whether what he had been told was "real" or "igh-level" rumor. It was described as occurring on the telephone 20 minutes before the president spoke with Mr. Begin.

The consequences of such a threat, if confirmed, would be destabilizing immediately and well beyond the war in Lebanon. In the circumstances, Mr. Johnson felt it would have been irresponsible to ignore his sources. Thus, the report was the first topic in a column previously planned and devoted to other aspects of the Middle East. It provided the basis for the headline: "The Phone Call Before the Phone Call May Hold the Key."

Interestingly, readers paid it more attention than the media at large. A number inquired. Yet, with one exception, Deputy Press Secretary Larry Speakes said last week that the subject had not been raised by any of the many news reporters -- including The Post -- who cover the White House.

Now, after asking his superiors he informs me the rumor was "absolutely untrue." Which may be all right as far as it goes, but questions remain as to what was the king's message in this call and an acknowledged earlier one.

Leaving unfinished business is old hat around newspapers and less a shortcoming than with television journalism. Still, like another failing -- herd journalism -- it can be no less disappointing.

Two other examples from The Post file:

At his Senate hearings for confirmation as secretary of state, George Shultz promised to respond in writing later to specific questions concerning the Middle East submitted by Sens. Rudy Boschwitz (R-Minn.) and Carl Levin (D- Mich.). From his oral testimony, Mr. Shultz was reported in The Post as emphasizing "the legitimate needs of the Palestinian people," criticizing the PLO to "get off the guerrilla kick," and committing himself to a "readiness to assure that Israel has the necessary means to defend herself." Some observers, including the senators, felt Mr. Shultz had insufficiently addressed the Camp David agreements and the Saudi Arabian plan put forward last year by King Fahd, then crown prince.

Mr. Shultz's responses were disclosed variously by the Senate Foreign Relations Committee and the Israel Public Affairs Committee, a leading pro-Israeli organization in Washington. The New York Times found enough newsworthy to report Mr. Shultz saying, "The Camp David framework agreement remains the only agreed basis . . . toward peace . . . . I do not favor any other approach." He virtually condemned the Fahd plan with, "it states conclusions which cannot be dictated."

Post readers were entitled to these views from the new secretary of state and haven't had them in these words.

And, back in April, I wrote the following to the editors: "This Iranian oil purchase story (1.8 million barrels at $29.51 per barrel) begged for more attention. Compare it with the Wall Street Journal and New York Times accounts of the same date. The Post story totally overlooked the 'first-purchase-since-Americans-taken-hostage' angle, hence its political context. It calls further attention to its inadequacy by saying why Iran is selling -- 'to boost its exports to help finance its 19-month old war with Iraq' -- without a word as to why the U.S. government feels the need to buy.

"Among others, the wife of a former hostage has expressed dismay at the paper's neglect. Maybe a peg could be found for taking the story further; maybe some editorial comment is warranted."

The story was restricted to four inches as a business "roundup" item. Since then, nothing. Truly, that's unfinished business.