Even those who can remember the past are condemned to seeing it repeated on television. "1968: A Crack in Time," the ABC News special at 8 o'clock Sunday on Channel 7, is a far cry from eloquent, but it marks a fascinating electronic milestone in the illusion business.

Through complicated new technique that executive producer Jeff Gralnick says combines chroma-key (simple superimposition) technology with something called Ultra-Matte, actor Cliff Robertson and correspondent Frank Reynolds, who narrate this retrospective on a monstrously eventfuly year, actually appear to walk back into scenes from the past and interact with them.

This gives a graphic new immediately to the old TV and radio phrase "You Are There."

"1968" marks the first time this technique has been used on a network news special, and while it may provide more flash than light, in this case, it certainly suggests intriguing new possibilites for television. Robertson strolls into a frozen shot from the old "laugh-In" series seems to mingle with the actors, walks up a stairways as if he were really there, and watches as the scene is set into motion.

Later, Reynolds appears to be getting off a bus in snowy New Hampshire for the '68 presidential primary there. He reports on Resurrection City, the makeshift poor people's protest community on the Mall, from inside one of the tents. Robertson stands in the middle of Fifth Avenue while a parade passes by.

In a program concerned with the assassinations, riots and war of a tumultuous year, it hardly seems justified to bring up yet again the fact that Robertson won an Oscar for playing "Charly" in the movies. Yet it gives the technicians the chance for their niftiest feat. Frank Sinatra had accepted the award for Robertson, then making a movie elsewhere, but now Robertson can go back in time and appear to grasp the trophy while standing behind the podium next to sinatra.

"It was quite a moment," says Robertson. "I wish I could have been there." And suddenly he is there, and an inexcusable self-indulgence has been made rather magical.

Unfortunately, producer Bruce Cohn got a little carried away with other electronic effects, including split screens, in telling the story of 1968, and the hour begins to seem a circus of gimmicks, many of dubious taste considering the grimness of the subject matter.

And yet, the content is foolproof; it cannot help but move us. Footage of Dr. Martin Luther King Jr., in his spellbinding oratorical style, warning that "we've got some difficult days ahead," are incomparably moving. This indeed was a year to break even the stoutest heart.

Despite the abundance of film available, however, and the technological wizardry at hand. Cohn and co-author Reynolds still didn't have the sense to trust the visual: their script is agonizingly overwritten, talky and trite. It's not enough that they open with the "sound and fury" quote from "Macbeth." Oh no. They also had to end with the inescapable Santayana quote about those who can't remember the past being condemned to repeat it.

Those who can't resist remembering that Santayana quote should be condemned to stop writing scripts.