FOR SHEER inanity, you could hrdly improve on the congressional campaign in the Eighth District of Virginia. There the euphonious Harris-Parris contest is hotly joined. The Republican candiate, former congressman Stanford E. Parris, has claimed credit for helping to kill a city wage tax on suburban commuters. But that is a total untruth, according to his Democratic opponent, the district's present congressman, Herbert E. Harris. So who did kill the tax?

As the commuters ride their Metro buses toward the District of Columbia from Virginia, perhaps their gaze will rise to the line of advertising placards above their heads. One of them offers an answer. "Herb Harris killed the D.C. commuter tax," the placard says, "and that saves you $300 a year."

Is there really anyone, except perhaps Mr. Harris' closest relatives and his staff, who believes that? In a committee meeting a couple of years ago, he cast a pocketful of votes, his own and some proxies, against a commuter tax bill. Mr. Harris can be said to have killed the tax only in the same sense that Mr. Parris did. All suburban congressmen and senators of either party, as well as all of the candidates who have ever run against any of them, are against thetax. The congressmen usually find ways, from time to time, to put themselves on the record. Since the suburbs have a lot of votes in Congress and the city does not, the voters of Northern Virginia can rest assured that -- regardless of the merits of the tax, and regardless of the election's outcome -- the prospect of a commuter tax remains dim to the point of invisibility.

If Mr. Harris and Mr. Parris cannot rise above these vacuities, they will invite the suspicion that neither of them is capable of debating anything more serious. If they continue to waste their time, and that of their listeners, quarreling over fake murders of no-hope bills, they will only persuade the Eighth District that neither of them is up to the job of representing it in Congress.