Normally a placid man, George Shultz erupted at a press conference in Belgrade when the Yugoslav foreign minister started making the usual flabby excuse -- that you have to take account of the underlying political "cause" -- for PLO terrorism. Hijacking, murder and torture, the secretary of state said heatedly, referring to the Achille Lauro affair, whose mastermind the Yugoslavs had helped to flee, are "not justified by any cause that I know of. There is no connection with any cause. It's wrong." Mr. Shultz even, it is said, turned red and banged the table.

No sooner had the secretary spoken, of course, than the usual fussbudgets started fretting that somehow his statement might have damaged relations. Think of it: A ranking Yugoslav had just had the gall to defend his untry's coddling of a criminal responsible for killing an American and terrorizing hundreds of other people. But, by the fussbudgets, that is not considered to be something that might damage relations. The murmured reprimand is saved for the fellow who says a plain and true word in response.

Think of this too: Few countries have been plagued more by terrorism, and face a greater menace from it, than Yugoslavia. As desperate as the regime may be for commercial or other reasons to ingratiate itself with Libya, Iran and Iraq, it should be among the last to go around making excuses for anti-Israel terrorism. For those same excuses -- they boil down to a stated need to treat the political "causes" -- can just as easily be invoked by the folks who regularly attack Yugoslavia's ruling communists. If the Yugoslavs do not have the courage to speak out against all forms of terrorism, they should at least have the discretion to stop apologizing for some.

A new rule needs to be engraved in everybody's mind: nobody who uses terrorism as a means is entitled to have his political purpose taken seriously as an end. Yes, those who use terror often -- though not always -- do so in the name of a political cause. In those circumstances, however, to reward the cause merely invites more terror. And as an increasing number of communist and Third World nations have found, this curse is not always limited to the world's designated pariahs.

The United Nations had another vote just this week categorically, rather than selectively, condemning an especially menacing form of terrorism, kidnapping. This is the right way. If George Shultz hears any more of the old two-faced apologies, let him bang the table again.