THE 1980 Democratic convention may provide us with a new political maxim: no city should be the host for a national political convention more than once in any generation.

Four years ago, practically every noisy and argumentative New Yorker seemed to have a) taken a total amnesia course (successfully) from Dale Carnegie and b) become overnight a happy extra from the best of Norman Rockwell's America. In 1977, New York enjoyed a surplus of friendly smiles and audible thank-yous.

This year is sadly different. Part of the problem may be the terrible weather: too hot and stickier than flypaper. But the earlier novelty of collectively transforming New York into Fort Worth for a week of courteous cordiality has lost its appeal. Dirty streets are barely visible under traffic so dense to make one want to organize a posthumous posse after Henry Ford.

It may, of course, not all be the fault of New York. The new maxim may instead, or in addition, be that, contrary to popular myth, the Democrats do not have more fun. Because, in a convention where security is very tight and a letter of credit is practically required to use the revolving door. Edginess has a floor pass and has been invited to every event.

It seems pretty sure that F(3)(c), nee 11H, will not join V8 or 4H or F15 as semi-permanent shotgun relationships of a number and a letter. In fact, F(3)(c) will probably be remembered by just about as many people as those who remember Rule 16c from the 1976 Republican convention. Forget, didn't you?

If there are some major or minor Democrats somewhere who have any doubts about supporting the national Democratic ticket this fall and if they have any unfulfilled ambitions about running for president as a Democrat and if they believe there is even a remote chance that Jimmy Carter could lose to Ronald Reagan, then they should at their first opportunity glance at the nearest political biography of Ronald Reagan.

There, the Democrats will read that Reagan's first major role in a national election was on Sen. Barry Goldwater's behalf in 1964. That year, an awful lot of Republicans who correctly foresaw the Goldwater defeat took a walk on the Arizonan. Non of them ever became a serious candidate for the Republican presidential nomination.

People, expecially people who vote in primaries and go to conventions, remember things like whether someone who wants to be president faithfully supported the national ticket.