TRUTH IS, we were all set to issue sober warnings of a second Mideast war, this one between Syria and Jordan, but in mid-afternoon yesterday the wires carried the urgent news that the would-be combatants had decided to call it off. It is indicative of the nature of Arab politics, at one level, that few people would have been surprised if Syria, acting out the various rages that animate it these days, had again attacked Jordan (its last attack, a fiasco, took place 10 years ago), and probably fewer still are surprised that the whole war scare suddenly blew over. There can be a lack of specific gravity to the exchanges that some Arab states (and not only Arab states) conduct with each other. Fortunately, no one got hurt this time.

The situation that remains on the ground is, as the diplomats say, interesting. Syria is out in left field, or at least it fears it is. The Assad regime has been beset by internal tensions that have taken hundreds if not thousands of lives in the past year, and it has felt so threatened by Egypt's peace initiative and Iraq's bid for Arab primacy that is has cozied up, riskily, to the two most distrusted countries operating in the region, Libya and the Soviet Union. President Assad evidently suspects that the Reagan administration may draw Jordan into an Israeli-Palestinian compromise that will leave Syria as Israel's only unmollified neighbor. He does not want to be ignored.

Nor should he be, if he follows the lead of President Sadat of Egypt and extends a hand of peace to Israel. Meanwhile, however -- and meanwhile is likely to be a long while -- he has, we hope, good reason to be suspicious of Kind Hussein. The king seems to sense an opening to get back into the diplomatic action on the West Bank, which he occupied before 1967. A new American administration is coming to power with the "Jordanian option" much on its mind. A like-minded Israeli administration could take over next year. The PLO is big at the United Nations, but that does not count for much in the real world.

In the latest flurry with Soviet-supported Syria, King Hussein reached out at once to the United States to demonstrate his own great-power connection. The Carter administration made the right noises in return. It is not at all a bad thing, at a moment of change in Washington, for the parties in the Middle East to be reminded of the value of a relationship with the United States.