Democrats who wonder whether Mario Cuomo is a wine that will not travel may have had their worries deepened when he recently delivered another speech in San Francisco.

His 1984 keynote address there was a smash hit in the convention hall and, presumably, Minnesota. His theme was that Democrats comprised a party of "caring." The implication was that non-Democrats do not even care, so Democrats have a moral monopoly.

In his return to San Francisco to address newspaper publishers, Cuomo made a valid point but made it with an off-putting tone. His point was that newspapers must be an affluent nation's conscience calling attention to persons left behind by prosperity. However, his additional message, intimated by his rhetorical mode, was that he is a member of the Compassionate Minority and that other people are not just mistaken, but also morally defective.

''Most Americans," he said, do not perceive clearly enough the ''huge part of the population" that is ''poor and in pain" and in ''sadness and despair." His message was: Most Americans, unlike your speaker, are unable to understand, or are indifferent to, an ocean of suffering.

He said the current prosperity "has been purchased at the expense of the well-being, the hopes and expectations of a large part of our nation, by the acceptance of such things as a level of unemployment that this nation would have considered a scandal only a decade ago." His message was: Today's prosperity has been achieved immorally, so people who do not feel ashamed, who are enjoying it, are morally obtuse. (By the way, unemployment today is 7.1 percent. A decade ago it was 7.7 percent.)

Recalling the 1984 convention, he said: "Surely those of us who were in San Francisco that year failed to convince the American people that we the nation had real problems." His message was: People who voted against Democrats did not just have mistaken ideas about the policies appropriate for addressing problems, they did not even have the elemental moral sense to know there are problems.

He said: "Over the last six years, the denial of compassion has been made both respectable and comfortable." His message was: Those who elected and reelected Reagan endorsed not just mistaken policies but moral callousness. As a Mondale voter told CBS the day after the 1984 election, the "country isn't good enough" to choose Mondale.

Now, someone who says, as Cuomo does, that Reagan policies are causing the middle class to "shrink" and its dreams to "wither" does not worry about nuances. Still, do Democrats really think that guilt-mongering and moral blackmail are the ingredients of successful electoral appeals? (On election eve Mondale complained that Republicans never used the word "decent," and he said: "I would rather lose an election about decency than win one about self-interest." There is a recipe for a disaster: Suggest that it is indecent to disagree with you.) It ought to be possible for a man of Cuomo's intelligence to call attention to problems without, in the process, seeming to disparage the public's moral sensibilities and to celebrate his own.

From the left and the right we are being bombarded by the rhetoric of people Joseph Epstein calls ''virtucrats." They are people who, no matter what else they say, always say "I'm fundamentally a damn fine person." Epstein, editor of The American Scholar, says the virtucrat is "a modern Diogenes who, in search of one good man, knocked off after turning his lantern on himself."

Epstein says that ''anti-war" and ''pro-life" are labels of virtucratic self-advertising, announcing that the holder of the particular political views is large-hearted and great-souled and obviously is opposed by people who are not just wrong, they are next door to depraved.

Today the right wing has its share of virtucrats of the ''when Jesus returns he will register Republican" sort. But Epstein says virtucrats are found more frequently on the left. People on the left, he says, seem to need to feel they are good-hearted, whereas conservatives are content to feel they are obviously correct. Disagree with a conservative and he will call you dense. Disagree with a liberal and he will call you selfish, insensitive and uncompassionate.

Virtucrats decorate their Volvos with bumper stickers that say ''you can't hug a kid with nuclear arms," a thought the policy connotations of which are unclear, but which clearly says: The driver of this car is an admirably caring person.

Honk, if you wish such people would go away.