Of the 3,141 counties in the United States, there were only two that before this month's election always had cast a plurality of their votes for the winning presidential candidate. Now there is just one. Recent elections have been hard on bellwethers. In 1968, Coos County, N.H., the northernmost part of the state, which includes the lumber mill town of Berlin, voted for Hubert Humphrey -- and fell off the list. In 1976 Strafford County, N.H. -- no stranger, either, to presidential candidates thanks to New Hampshire's first-in-the-nation primary -- went for Gerald Ford by exactly three votes and lost its bellwether status.

This year's battered bellwether was Palo Alto County, Iowa, a 30->by 30-mile square of northern Iowa farmland. Palo Alto (named for a battle in the Mexican War fought just before Iowas counties were laid out) is smack in the middle of farm-revolt territory, and in recent years has been more Democratic than the national and Iowa averages. It lies just 30- some miles south of Elmore, Minn., where Walter Mondale grew up.

So two weeks ago, when Iowa came within 3 percent of voting for Mr. Mondale, Palo Alto County gave him 53 percent of its votes. Asked to explain why, a county official said local voters "felt the way everybody else should have felt." Which is to say that Palo Alto has given up on being a bellwether.

That leaves Crook County, Oregon. If you wanted to choose a single county that always voted for the winning presidential candidate, you could hardly find one geographically more remote or sociologically less typical of an increasingly suburbanized and quiche-ified nation. With a history of Indian raids, sheep and cattle wars and vigilantes, it seems more the America that was than the America that evidently is to be. Crook County (pop. 13,091) is lumber territory, with some cattle ranching, smack in the middle of Oregon, 160 miles from Portland; its one incorporated city, Prineville (pop. 5,276), sits on the Crooked River.

Oregon's lumber industry has been in trouble in the recession, and the state itself gave Walter Mondale a fairly good vote. But Crook County gave Ronald Reagan 62 percent of its votes, maintaining its bellwether status. There's been lots of controversy over the television networks' practice of projecting the results in some states while the polls are open in others, but through it all, no one has suggested one alternative way of presaging the result: station exit pollers throughout Crook County. It's guaranteed to give the correct result -- until the day this bellwether, like all the rest, ends up sounding a false note.