Exhibit helps Dallas come to grips with JFK slaying. Stream of visitors to site has attested to world interest in historic event

The grassy knoll looks very much the way it did 25 years ago, but the old book depository building is now a county government facility - except for the sixth floor. Grassy knoll, book depository, the sixth floor - these words retain strong connotations for many of the 130 million Americans who can recall Nov. 22, 1963, the day President John F. Kennedy was assassinated in Dallas.

Twenty-four years later, Americans and foreigners still flock to the site where one of the most traumatic historical events of their lifetime occurred. On any given day, scores of them can be seen surveying Dealey Plaza where the Kennedy motorcade passed, or counting the floors up the fa,cade of the former Texas School Book Depository building to the window from which official investigations say Lee Harvey Oswald fired the fatal shots.

Dallas, a can-do city with a highly optimistic outlook, has never cared to highlight what is probably the darkest day in its history. The sixth floor of what is now the Dallas County Administration Building sits vacant, a chain-link barrier protecting the alleged assassin's corner perch from souvenir hounds who had begun chipping off red-brick fragments of history.

Within a year, however, the sixth floor is expected to open to thousands of visitors annually with a permanent educational exhibit on the assassination and its effect on the world. Supporters say they hope the exhibit will provide access to history - something the daily visitors obviously want.

And although not everyone in Dallas is enthusiastic about the project, there is a feeling that it is time to acknowledge an event that for years many Dallasites tried to forget.

``Let's face it, it's not the kind of event that a city can point to with real pride,'' says Thomas Knock, a 20th-century historian from Southern Methodist University here. ``But an exhibit like this is inevitable, and I'd say the assassination is probably far enough in the past that people can come to grips with it.''

The $3.5 million project will be financed in part by county revenue bonds - to be used primarily for construction of a special elevator to take visitors directly to the sixth floor - and partly by private donations.

Not all the city's leaders stand behind the project.

``If what they're planning hasn't seen completion, then maybe not enough people want it done,'' says Stanley Marcus, a prominent civic leader and president emeritus of Neiman-Marcus. Although he was involved in construction of a monument to the slain President on a downtown plaza, Mr. Marcus says he finds the exhibit ``appeals to a certain morbidity rather than a celebration of a person's life.''

But active participants in the project say the city's feelings about the exhibit have changed, and are now supportive.

``We were ready with plans about five years ago [when an earlier fund drive stalled], but that may have been a bit too soon,'' says Lindalyn Adams, president of the Dallas County Historical Foundation, which is spearheading the exhibit. ``I think most Dallas residents now see the assassination in the perspective and light of history.''

Mrs. Adams says that for years the last thing many Dallasites wanted was a display drawing attention to an event that had blackened the city's reputation around the world.

For a long time many city residents found they could not travel without being scorned, refused service in restaurants or rides in taxis if their residence was revealed, according to Adams. While such close association with the assassination has long since been replaced by more contemporary associations with the Dallas Cowboys and the Dallas of TV's J.R. Ewing, it has not been erased.

Despite delays in completing the project, Adams says she believes it's being done as quickly as the city can accept it. ``We live in an era of instant history,'' she says. ``We are doing this much sooner than, say, the Alamo was done or the Gettysburg battlefield.'' Ford's Theater in Washington, where President Lincoln was assassinated, was not open to the public for more than a century after Lincoln's death.

Project coordinator Conover Hunt says she wants the exhibit to help visitors understand the effect one very emotional experience had on the world. ``There is some indication people changed even in the kinds of jobs they wanted after this,'' says Ms. Hunt. The perception of Europeans changed about America as a world power, she adds, and the perception of Americans changed about themselves.

As Hunt discusses the project, a bus pulls up and drops off some foreign soldiers who want to view the site. ``For millions of people, coming here is a powerful emotional experience because it's an important part of their personal history,'' she says. ``What we're trying to do is give them access to it.''