Now, dear reader, here's a proposition: Every day you've got to determine, if you read us at all, what's true, what's false, and, as in most cases, what lies inconclusively in between. Witness today.

Elsewhere in these pages, you'll find a column by our colleagues, Jack Anderson and Les Whitten. It begins with the riveting words: "The FBI has quietly entered the investigation of another presidential assassination - this one the 112-year-old shooting of Abraham Lincoln . . ." The column goes on to say: "The belated FBI inquiry into Lincolin's death may help to resolve such mysteries as these: Was Lincoln the victim of a secret conspiracy reaching into his own cabinet? . . ." Credit for this monumental investigation ("new light on these questions") is given to "some 18 pages that mysteriously disappeared from Booth's diary but may now have turned up." And: "Now an indefatigable American expert, Joseph Lynch of Worthington, Mass., has found what appears to be the missing pages."

Not having much else to report in this most normal summer since the '50s, which is to say dull, aside from the recent discovery of that long-extinct prehistoric monster, the plesiosaurus, from the murky depths of the southern seas off New Zealand, or a sociological examination of the deeper significance of the latest phenomenon, the film "Star Wars," we turn now to that burning question - not who killed Kennedy, but who killed Lincoln. And also how that subject happens to surface in the press this first week of August, '77.

The American expert, Joseph Lynch, lists his address as P.O. Box 72, Worthington, Mass. His phone, the operator says, has been disconnected. A day of indefatigable tracking led from Worthington, Mass., to Salf Lake City, Utah, and ended at the Steamboat Square Book Shop in Albany, N.Y., where Mr. Lynch was said to receive messages. "He's a very private man who jealously guards his privacy," the proprietor said, cautiously. Mr. Lynch maintains a phone in the Albany area, but it, too, is unlisted. Finally, late in the day, after more enterprising investigative reporting, the elusive Mr. Lynch himself was on the phone.

"I'm always interested in the subject of, shall we say, Americana, the artifacts of history," he pronounced, in a Brooklyn accent. "One might call me a dealer-collector. In general, I know a lot about American history. It's the thing I liked best in school. I'm not a liberal in my politics. No one's ever accused me of being a Communist. If anything, I'm conservative in my views, I'm totally amateur, I admit. My education is limited to high school and the business arena, as we know it - making a living from one day to next. I'm not Charlie Big Bucks, either."

Mr. Lynch then proceeded to tell the following story:

Some 3 1/2 years ago, he was conducting an inventory and appraisal of papers in the possesion of heirs of Edwin M. Stanton, Lincoln's secretary of war. As is his custom, he read out a description of various letters and manuscript pages into a tape recorder. Among the papers were some 18 pages of handwriting, which seemed to have been torn from a diary. In checking into the contents, he determined that these were the missing pages from John Wilkes Booth's diary. No matter how. He did.

In the course of his work, he happened to mention his discovery to another dealer, who in turn passed it on to another, who in turn . . . Anyway, you get the picture: The word was out.

Fast curtain, exit Mr. Lynch, enter a David Balsiger, end act one. Plot thickens.

David Balsiger was in the East researching a movie on "The Lincoln Conspiracy," to be produced by Sunn Classic Pictures, with offices in Salt Lake City and Los Angeles. Sunn Classic describes itself as "a unique family film company." In its promotional material, Sunn says of itself: "Before starting a picture, this innovative company locates the special group of people who will enjoy that particular kind of film and then shapes it to their preferences like a custom tailor."

In other words, it uses the modern techniques that serve us in everything from selling cigarettes to politicians: mass market research, polling, computer readouts to determine what the audience wants. Then it makes the films. "Docu-dramas," it calls them. Some of Sunn's credits, for film and TV: "The Life and Times of Grizzly Adams," "The Mysterious Monsters" and "The Amazing World of Psychic Phenomena."

The company modestly claims "The Lincoln Conspiracy" will uncover "the most shocking historical conspiracy of our times." It's sort of a Watergate-revisted, before Watergate ever happened, of course. The seeds of the crime, and so forth. Watergate lives. And sells. Even before the fact.

David Balsiger, described as "an investigative snooper" by the company, was doing the gunshoe work that all reporter-researcher investigators must do when he stumbled on a lead.

He says he was in Washington, D.C., at a Civil War type gun show, when he heard about an Americana collector who had found the missing pages from Booth's diary. "It took me nearly six weeks to track Lynch down," Balsiger says. After calling dealers from New York to Boston, he finally got a call back. He and Lynch began negotiations over the material. And here, if it hasn't already, the story becomes too complex to unravel at this writing. But the essence:

Balsiger says Lynch estimated the value of the material at a quarter of a million to a million dollars, and that Lynch, acting as the middleman for the heirs, first put a price of a quarter million on it. Lynch denies this. The Stanton heirs he says didn't want to deal with anyone. "So far as they were concerned, the diary was a black spot on everyone concerned," he says. That is, Stanton clearly was implicated as the master conspirator. How would you like to be known as a direct descendant of the man who had Father Abraham slain?

In the end, Lynch sold to the movie company a transcript of the supposed diary, made from his tape-recorded descriptions. The price was somewhere between $5,000 and $10,000. The movie company claims to have done exhaustive work into authenticating the pages. They were evaluated "by historical experts," and by other means. Voice analyses were performed on numerous taped interviews "using the psychological stress evaluator (PSE), a 'truth' machine used by law-enforcement agencies and the CIA."

Now you must understand one fact: At this point no one has seen those newly round pages. No one has met the Stanton heirs. No one, aside from Lynch, knows who they are, or where they live. And they aren't talking. Too much bad publicity, too much embarrassment to the old family name.

"And what about that FBI investigation?" you ask. Read on. Denouement to come.

Sometime last fall, Michael (Mike) Harmon, curator of the Ford's Theater Museum, got a call. It might be worth his time to contact a film company, Sunn Classic, in Salt Lake City, he was told. Seems new material on the Lincoln assassination had been turned up. New material is always turning up, but Harmon made the call. In time, he met Lynch, Balsiger and other people from the movie company. One of them asked for, and got, permission to photograph the original Booth diary on display in the museum. There had been rumors, among the hordes of Lincoln assassination conspiracy buffs, that Booth's diary contained "invisible" writing. The keys to the case.

After that, Harmon says, the government decided to protect itself. "We asked the FBI to examine the diary in our possession to alieviate any future uncertainty as to its authentieity, or any questions pertaining to 'hidden' writing." That was done. The diary is now back in its case in Ford's Theater.

The FBI has never looked at the "missing pages" from the diary. As Harmon says: "Being a cautious historian. I have to say this: The burden of historical proof rests on Lynch. If a guy says, 'Hey, I have the documents that say Mary Lincoln did it,' it's the burden of that person to produce the documents in question. The only way anybody's going to be able to determine their authenticity is when they become public documents subject to public scrutiny and examination."

Harmon's a Civil War buff himself. He recalls being fascinated by an event a year ago.Lincoln's wallet had been sealed inside a box maintained at the Smithsonian. It was opened during the bicentennial celebration. Guess what they found.

Five dollars - in Confederate money.