UNTIL 20 YEARS ago, Maine, alone of the states, held its general election in September on the eminently logical grounds that Maine voters should not have to battle November blizzards in order to vote. This September-voting produced one popular (and almost always inaccurate) political chestnut: "As Maine goes, so goes the nation." The chestnut was thoroughly and famously roasted by Franklin Roosevelt, whose 1936 landslide left Vermont the only state following Maine into Republican Alf Landon's very lonesome camp.

Last Saturday, some 1,300 Maine Republicans, chosen in town caucuses, assembled in Portland for a "Maine Republican presidential forum." As is quickly becoming customary at all such party gatherings, an informal, unofficial, non-binding, straw balloting was scheduled. This is the vogue. Witness the Iowa Democratic dinner in Ames on Saturday where President Carter won the non-binding vote by a very comfortable margin over Sen. Edward Kennedy. Sen. Kennedy, apparently anticipating the Carter show of strength, chose not to dine in Ames. Instead, he spent the day in Buffalo and West Virginia so as to draw attention from President Carter's straw victory.

The only reason anybody outside of Portland knew about the Saturday Maine event was that Sen. Howard Baker's presidential compaign staff had told several dozen political reporters that this would be the just-announced candidate Baker's first "win" on his long, victorious march to the republican nomination and the White House. And the several dozen reporters conscientiously told the rest of us.

But somebody did not tell enough Republicans in Portland. Those New England Yankees proved to be unpredictable and disproved the idea that political popularity is transferable -- in this case, the popularity of Maine's Republican Sen. William Cohen, who had endorsed and supported Mr. mBaker. Demonstrating that candidate endorsements are more interesting to politicians than important to voters, the Maine Republicans chose Ambassador George Bush over Sen. Baker (by 20 votes). Sen. Cohen confirmed, to his temporary political embarrassment and personal surprise, that in American politics in 1980, nobody delivers. We do not generally deviler groceries or milk anymore, and nobody, including a very popular U.S. senator in a very small state, delivers votes.

So 1,300 Maine Republicans -- or, more precisely, 466 of them -- have given Mr Bush's campaign a temporary lift and Mr. Baker's campaign a temporary reversal. And that's the situation until the next informal, unofficial, non-binding, stray balloting is held somewhere by a few dozen registered Republicans or Democrats and is reported by a dozen or more political journalists. David Keene, Mr. Bush's campaign director, brought welcome candor and perspective to his post-mortem of the Bush-whacking of Mr. Baker when he said: "remember all that stuff we were saying earlier in the week about this not being important? We were wrong."