ON TUESDAY NIGHT, unless Gov. Charles S. Robb acts to postpone or commute his sentence, Frank Coppola will be executed for the 1978 murder of Muriel Hatchell in Newport News. It will be the first time the electric chair has been used in Richmond in 20 years, and only the fifth execution in the country since 1967.

There is little reason for sympathizing with Mr. Coppola. His crime was a vicious one--beating a woman to death in the course of robbing her home. And there is plenty of reason for sympathizing with the governor who, in the words of an anti-capital punishment organizer, is in "the most no-win situation a politician could be in." Gov. Robb, after all, had no part in meting out this sentence, yet he is the only one who can prevent its being carried out. He supported the death penalty during his election campaign, and this position is thought to be a popular one in Virginia. The path of least resistance for the governor at this point would be to do nothing and simply to allow Mr. Coppola to die.

He shouldn't do it. As he wrestles with this terribly difficult decision over the next few days, the governor should keep three things in mind: proportionality, procedure and principle. Just last week, we expressed our strong disagreement with a sentence for murder in Kansas City, where a man received a 60-day term for beating his wife to death and dumping her body in a lake. The penalty seemed wildly out of proportion to the crime. Yet the offense was similar to that committed in Newport News. In 15 states there is no death penalty at all, even for multiple murder. In the other 35, standards vary widely, as does the frequency with which the sentence is imposed. It is, in part, this lack of a national, uniform sense of proportion between crime and this ultimate punishment that troubles the Supreme Court, and that should give every governor pause.

Moreover, the procedures in the Coppola case have an unfinished quality about them. Mr. Coppola, a former policeman and Catholic seminarian, has consistently maintained his innocence, though he was, of course, convicted by a jury. He has refused his attorney's permission to proceed with appeals so that, in spite of the severity and finality of the sentence, the full judicial process has not been completed. In addition, Virginia's death penalty statute, enacted in 1977, has not yet passed muster in the courts. A case challenging the law is now on appeal in the Fourth U.S. Circuit Court. If it is invalidated some time after Tuesday, it will be too late for Mr. Coppola.

Finally, the governor must be guided by principle. If the taking of a human life is the most unacceptable of crimes, can it ever, at the same time, be an acceptable penalty? Do we, in the last quarter of the 20th century, want to reinstitute a barbaric procedure that had all but disappeared in this country? Gov. Robb, like all Americans, has heard the argument and searched his own conscience. We believe on principle that society should not sanction this kind of killing under any circumstances. Even if the governor does not subscribe to this fundamental position, however, there are a number of other reasons to stop this particular execution, and he should do so.