Three's company, four's a crowd.

GUESS WHO'S trying to build a "global empire"? No, not the Soviets, silly! It's Rupert Murdoch. The Australian-born "press baron" (as distinguished from "publishers," who are liberal) is slated to buy a set of seven major metropolitan TV stations from Metromedia Inc. Over the last few years, Mr. Murdoch has emerged as pro-capitalist and anti-Communist, and not everyone in the media welcomes his interest in television. As a matter of fact, a lot of self-styled pluralists who sing the praises of the melting pot of Irish, Italians, Jews, Asians, and blacks seem to be drawing the line at Australians. Jimmy Breslin of the New York Daily News refers to Mr. Murdoch as "the Alien."

In a way it was understandable that media people should have been anxious about Ted Turner's attempt to buy CBS recently. Apart from his political views, Mr. Turner would have probably shaken things up internally. Some people stood to lose positions they now hold.

The Murdoch case is different. The TV stations he has picked for purchase aren't network affiliates; he even aspires to create a sort of fourth network. He would add, not subtract. But by doing so he might just expose--and destroy--the media monopoly of liberalism. Without laying a hand on the big three, he would make them all look different. They sense this, and they fear and resent it.

From their point of view, their worries are justified. And for just these reasons, it would be a great watershed if either Ted Turner or Rupert Murdoch were to control or create a major network. The trouble with Murdoch, in liberal eyes, is not that he's Australian; it's that this "Alien" is pro-American.