One well could feel that it should never have taken place and yet be glad to have seen it -- the debate on South Africa between the Rev. Jesse Jackson and the Rev. Jerry Falwell televised last night on the ABC News program "Nightline."

Neither man could ever pass for the greatest living expert on South Africa, so why were they teamed in debate? Largely because of box office potential, it appeared. When the two first sparred over South Africa on ABC's "Good Morning America" on Aug. 21, the telegenic sparks flew. So they were invited to continue the colloquy on "Nightline," with anchor Ted Koppel moderating.

Viewers were primed to expect a clash by night. The possibilities for heat were far greater than those for light during such an encounter, and frankly more tantalizing. Yet Koppel felt the need to pull in the reins on both men when they became most heated in their remarks, Falwell accusing Jackson of "hypocrisy" in refusing to condemn Soviet interference in the affairs of African nations, Jackson accusing Falwell of "Communist Red-baiting."

Koppel early cautioned the two men "not to launch personal attacks" on one another, yet the prospect of personal attacks seemed one of the more exploitable elements of the show. These came in the second half of the one-hour (and thus too long) debate, when Jackson accused Falwell of suggesting the Rev. Martin Luther King Jr. was Communist-supported and Falwell accused Jackson of making favorable comments about Che Guevara, Fidel Castro and other famous hemispheric Commies.

Another highlight of sorts was when Jackson declared that "Pharaoh and Herod" were not Communists but Fascists. Also, at one point, Falwell philosophized, "Sometimes we must deal with a skunk occasionally who is our friend."

Around and around they went, all rather predictably. A viewer might well have gotten the impression that Koppel was more authoritative and knowledgeable on the subject of South Africa than the two battling reverends. On the other hand, his attempts to dignify the meeting and keep it orderly seemed cold water thrown on a compellingly volatile contretemps.

Broadcasts like this one have served to elevate Falwell to a dubiously justifiable position as a national spokesman on governmental and international issues. Jackson at least was a bona fide candidate for president; Falwell is a preacher with a vast television ministry. Time and again network news producers call up Falwell for appearances on such programs even though his qualifications to speak on such subjects remain questionable. When it comes to making TV guest shots, Falwell apparently never plays hard to get.

The Falwell-Jackson debate was doomed from the start to be insubstantive, repetitious and finally rather irrelevant. But personalizing and polarizing the issue in this essentially sensationalistic way unquestionably does draw increased national attention to the subject and give it additional prominence in American conversation.

In other words, everywhere the ABC network has affiliates in this country, people are going to be talking today about the Jackson-Falwell debate of last night. That can't be bad, no matter how inappropriate the debate itself was.

At the end, the two men shook hands. They had at least agreed, several times, that the policy of apartheid was a "cancer" but differed on the ways to remove it. Throughout the program, Falwell referred to Jackson as "Jesse" or "Mr. Jackson," but never or rarely as "Reverend Jackson" ("You're making reckless statements, Jesse"); was this an indication of hauteur and disdain? Jackson was generally more dignified. He referred to his fellow debater as "Reverend Falwell" and did a better job of keeping his cool.

Occasionally Koppel's firm hand was more helpful than hindering. When Falwell reached into a pocket for some sort of back-up printed matter, Koppel made him stop. "Don't start reading anything," he warned Falwell. When Falwell persisted and donned reading glasses, Koppel said, "Take your glasses off, if you would." Ted's a toughie.

The "Nightline" staff produced informative and dispassionate "glossary" inserts that summarized and explained basic components of the South African situation. "Nightline" has done many programs on South Africa. With the exceptions of the staff-produced inserts, this was one of the least informative, yet it is the confounding nature of television that it will probably also prove to be one of the most watched.

As time ran out during one segment, Koppel told his guests, "There's something called a commercial imperative and we just reached it." He meant it was time for another break. But it was plenty clear by this point in a largely pointless exercise that it was the commercial imperative that had brought the two debaters together on national television in the first place. Reason, logic and good sense cry out for there not to be a rematch, but showmanship usually prevails in television, so there probably will be one anyway.