Mervin Field is a respected pollster, and nowadays he brings with him the dolorous news that our president has slipped so far in the electorate's esteem that, were the presidential election held now, Jimmy Carter might finish third behind Ronald Reagan and the good Parson Anderson. True, things could be worse. Our president could be trailing Ed Clark, candidate of the Libertarians, and Barry Commoner, candidate of the Chicken Little coalition. But then the voters really have not had a chance to compare our president with Clark and Commoner. Let him stumble into a televised debate with them and his goose will be cooked and scorched, and left on the compost pile.

So gloomy are our president's prospects that many a Democratic officeholder now dreams of liberating the delegates at the Democratic convention from their vows. It is a fabulous dream: Throughout the vast Madison Square Garden a heavenly host suddenly strikes up "Happy Days Are Here Again." The assembled patriots banish Jimmy to the family gas station. His entire Moon Pie mafia departs also. Ancient wheels begin to turn. Cigar smoke, the like of which has not been whiffed at a Democratic convention for a generation, suddenly fills the Garden. There is a noble speech, and in a burst of exultation a shining new Democratic messiah leaps forward -- an FDR for the 1980s! Once again the public trough is preserved for the statesmen and flunkies from the Party of the Big Heart.

Alas, the dream is sheer delusion, self-induced and thus all the more reprehensible. After all, these are not the Democratic delegates who nominated FDR. They are not even the Democratic delegates who nominated JFK. These are the delegates who nominated George McGovern and Jimmy Carter. Today they are older and even more muzzleheaded.

During the past decade and a half, the Democratic politicos have been the herders of hysterics. No goofball constituency has been too exotic for their cynical roundups. Every zany with a gripe has been encouraged. At this convention the bewildered remnants of the old New Deal coalition will sit cheek and jowl with the friends of the furbish lousewort, vegetarian activists, advocates of rights for trees, militant homosexuals, sworn opponents of the Fortune 500, stalwarts from the National Education Association and worse. The affair could become too violent even for prime-time television. No wonder Sen. Henry Jackson planned not to attend. Even Sen. Frank Church wanted out.

Imagine the results the Democratic wheeler-dealers might stick themselves with if they were to open this convention to the will of these delegates. The nonsense of the 1972 orgies would appear tame and civilized by comparison. One sees Bella Abzug brought back to life. One sees Ramsey Clark grasping at the purple. The disciples of Jerry Brown and Ralph Nader bargain furiously. It would be the gaudiest, gassiest, most colossal political convention ever held. However, it would bring certain defeat to the Democratic ticket in the fall and, if enough taxpaying Americans got to see it on television, it might lead to the outlawing of the Democratic Party by order of an outraged citizenry.

It the truth be known, candidate Carter is just about what one might expect from the modern Democrats. His policies on defense, the economy and social engineering are firmly rooted in their sacred dogmas. For years they have been winning elections by buying off ever larger chunks of the eletorate. Their foreign policy has consisted of thundering highfalutin orations toward the agape foreign ministers of the world, while swinging whiffle bats at tyrants and shipping the national wealth to ingrates and friends indiscriminately.

Now the bills for all their extravagances are coming due, and they extravagances are coming due, and they blame Jimmy Carter. It is a shameful interlude, and my preisdent has every right to feel hurt. He may be ready for the morticians, but he was condemned to death by the Democratic dogmas. Let us not blame his passing on the Libyan butchers, their bankers or Billy.