Some people are still arguing the whys and wherefores of the Cuban missile crisis. So it's not surprising that skeptics instantly started second-guessing the Reagan administration's latest dust- up with Libya's Col. Muammar Qaddafi-- that's in the nature of gunboat diplomacy, now known less romantically as deterrence.

When it works, the first question is whether there was anything much that needed to be deterred. The next question is whether the gunboats--in this case, the dispatch of four AWACS reconnaissance planes to Egypt and the movement of U.S. naval forces to waters off Libya--actually did the deterring.

And so there's been a lot of rooting around in the record of who said this or that --what did the president know and when did he know it? At his press conference last week he didn't seem to know much; what he actually said (that the AWACS planes were on routine training exercises and that there had been no "naval movement of any kind") wasn't accurate.

While "high White House officials" tried to rescue the president, "informed sources" at State and Defense were describing in vivid detail an intricate Qaddafi plot to assassinate Sudan's Jaafar Nimeri and his chief lieutenants, seize the airport at Khartoum and clear the way for Libyan troops to land and consolidate the coup. Meantime, officials in Egypt and Sudan were saying it was no big deal-- even as Washington sources reported authoritatively that Egypt's President Hosni Mubarak had specifically appealed for a U.S. show of force.

It sounded fishy, the more so when you cast it in the context of the vendetta that this administration has had going with Qaddafi from the start. Not that the Libyan strongman hasn't done more than enough to qualify for the title of "international terrorist"; but to Alexander Haig he was the No. 1 international nasty, a worthy test of a superpower's power.

You have only to recall what Ronald Reagan made of the "Battle of the Gulf of Sidra" in 1981, when two outgunned Libyan jets mindlessly attacked a pair of U.S. Navy fighters and were quickly dispatched. From the deck of a carrier off the California coast, an exuberant Reagan held forth: "Let every friend and foe alike know that America has the muscle to back up its words."

So one had to wonder whether the administration wasn't again making a big deal out of a little deal--except that this time, with only a few excesses, the performance pretty much fit the public relations.

My guess is that Mubarak did have reason to believe that Qaddafi had a coup working against the Sudanese; that he received about the right amount of U.S. reinforcement; that a plot was nipped. More important, the Reagan administration seems to have a more realistic perception of Qaddafi than it had two years ago. "The net of the whole thing," said Secretary of State Shultz, "is that the president . . . acted quickly and decisively and effectively, and at least for the moment, Qaddafi is back in his box where he belongs."

So why were the Egyptians and the Sudanese playing it down? The answer takes us back to the nature of gunboat diplomacy: a form of communication that is not all that easy to fine-tune. The Reagan administration had the usual incentive to celebrate what appeared to be a useful piece of work--though not in the chest- thumping style of the Haig days. The incident sent a useful message to Qaddafi and the rest of the world.

But Mubarak, in particular, has a different international public relations problem; he is seeking to restore Egypt's pre- Camp David position in the Arab world. He also fancies Egypt as a force among the nonaligned. Highly visible military-strategic collaboration with the United States doesn't help.

Neither does gloating. Anwar Sadat was given to putting down Qaddafi as "that child--that mental case next door," on the theory that to build him up as a threat would only make him look bigger.

So what we have been witnessing in the apparent discrepancies in what is being said in, say, Cairo and Washington is not so much a conflict of purpose as a conflict of interest in publicity.