If America had a middle aisle, Americans would be rolling in it, their ribs squeaking from laughter. The other six are not, after all, to be the only onions in the Democratic stew, which is like Irish stew in that almost anything tossed in just makes it more savory.

It is hilarious -- unless you do not find amusing the trivialization of the world's oldest political party and most important political process. Chortling Republicans should remember that cynicism is an acid that cannot be hermetically sealed on one side of the partisan divide: the political vocation generally is being devalued.

Gary Hart is back and standing tall because, he says, of his ideas, such as "strategic investment economics," which other candidates have inexplicably neglected, and because "other national leaders" have not entered the race since May. But who is Hart to be so dismissive of the other six, three of whom (Jackson, Dukakis, Simon) have much more support than he had at this point in the 1984 contest? Four years ago he was at 3 percent, about where Gephardt and Gore are.

"Sometimes," said Hart in New Hampshire, "the best thing to do is what you feel you must do." Must. Like Martin Luther at the Diet of Worms, Hart says, "Ich kann nicht anders." He cannot do otherwise because of the lash of necessity -- duty.

And what words are emblazoned on his banner? "Smaller Aircraft Carriers"? Stand back so you do not get trampled in the stampede to enlist in what he calls his "cause." Hart has ideas, but so do the six -- similar ideas. What nowadays distinguishes Hartism is generational vanity on the part of people like Hart who claim (as Hart put it in his gaseous speech to the 1984 Democratic National Convention) that people who were young in the 1960s have ''a unique bond of tragedy and triumph.''

Seriously, folks, looked at from his vantage point -- from that cabin in Troublesome Gulch, Colo. -- what is the downside to his decision? He is not giving up a Senate seat or anything else. He wants a ''forum'' and the lecture circuit has been lukewarm. He may get some federal money and may shed his reputation as a welsher on his debts.

Having been restlessly moving around the country for 16 years, he must have suffered an excruciating case of cabin fever and decided to write a different end to the Gary Hart Story. And speaking of writing, perhaps he has writer's block. You may remember that he said he had a hankering to hole up in humble surroundings and write novels.

Anyway, Hart is running because, aside from the literary life, running is what he does. But, you say, he may be humiliated? How -- by more stories about assignations? You have not been listening to him. The Democratic Party has found its Spiro Agnew.

Hart's newest new idea is to run against the press. But he is a deep, somewhat soulful, intellectual, more-in-sorrow-than-anger Agnew, sad because the press is insufficiently interested in ''the issues.''

There is one more reason why he is running. He thinks he can be president. There already have been three front-runners in Iowa, so who can say that lightning will not strike. Put Hart in a debate with the other six and he will look impressive enough. He has the almost manic composure of a person completely obsessed by a quest.

Hart's support should be construed as 2 percent an endorsement of smaller aircraft carriers (and strategic investment economics) and 98 percent a vote for ''anybody but any of the others,'' a collective repudiation of the six. The pressure will now mount for Mario Cuomo to say: I said, and meant, that the six are embryonic Lincolns, but Hart should not be the head of the party, therefore . . .

Hart could also injure the Democratic Party by helping Robert Dole. Dole has needed a strong Democratic front-runner to make his case for being more electable than George Bush. Suppose some polls show Hart beating Bush. Suppose Hart causes Cuomo to reconsider.

In a recent poll, Dole had a higher ''favorable'' rating among Democratic voters than any of the announced Democratic candidates. Although Dole is sometimes portrayed as the Doberman pinscher of the GOP, Bush is more polarizing: his favorable/unfavorable rating reverses when Democrats rather than Republicans are polled.

However, Republicans laughing today may not laugh last. The commotion Hart has caused does dramatize the ''none of the above'' mood that could produce a brokered convention in Atlanta. If the Democrats go marching out of Georgia behind Sen. Sam Nunn, they win.