I've just finished a long conversation with a man who may be close to unique among my black friends. He says he's going to vote for Walter Mondale.

No, I haven't fallen in with evil companions of the right. Except for a handful of freethinkers and a couple of curmudgeons, almost all of my friends will vote against Ronald Reagan. But they will put their checkmark beside the name of Mondale not as a vote for the Democratic candidate but as the only practical way of voting against the Republican.

My friend the Mondale backer is different, knows he's different and has a good deal of trouble understanding why this should be so. He reminds me that in spite of the celebrated Reagan recovery, Americans -- and not just black Americans -- are only about as well off as they were before the eagan recession; that interest rates and joblessness are about where Reagan found them; that aside from a real decline in inflation, the economy has not improved under Reagan. So why, he wonders, is there so little enthusiasm for Mondale?

He is particularly bothered by the defection from the Democratic Party of blue-collar workers (including those in the older, economically depressed industrial states) and by young college students. Why is this happening?

We spent an hour and more shooting down each other's theories, without reaching any real consensus.

He thinks he senses a resurgence of racism, as evidenced by white desertion of the party identified with the interests of blacks. I agreed that such black interests as new programs for the disproportionately black "underclass" and support of affirmative action seem far from the consciousness -- and conscience -- of white America. But is this a resurgence of racism?

I tend toward a slightly different explanation. First, with regard to programs for the poor, America has finally come to believe what advocates of the poor have been screaming for years: that the programs don't work. (You ought to go back and read some of the annual statements of civil rights groups during the Carter years and earlier, declaring black economic progress a myth and the programs designed to promote it a complete failure.) I also think that white America has concluded that there has been enough affirmative action, at least of the sort that gives preference to black applicants.

Voters, including college students who are too young to have had their consciences molded by the idealism of the civil rights movement and blue- collar workers who fear for their own future, are no longer interested in racial altruism.

My friend will buy at least a little of that explanation. But, he says, it still doesn't explain the lack of enthusiasm for Mondale, even among blacks. What does?

I could answer only in terms of my own mental processes. I have been following the campaign fairly closely, hearing the speeches, reading the statements, listening to the debates, and I have only the vaguest idea of what a Mondale presidency would be like. He would, I assume, be "fairer" than Reagan, and more concerned about the plight of black America. But I couldn't begin to guess how that would translate into social programs, legislative proposals or economic policy.

The one thing I am sure of (and it sounds like a Reagan cheap shot) is that he would raise taxes in order to reduce the federal deficit. That needs doing, but it hardly suffices as an economic program. He would, I suppose, be more likely to negotiate arms reductions (which is good) and less macho (which may or may not be good). But will he make the economy better? And if he doesn't, would his sympathy for blacks be all that helpful?

I join my friend in rejecting much of Reagan's vision of America, but it bothers me that as long as I have known Mondale, I have no real sense of what his vision of America is. It's easier to be enthusiastic about ending Reaganism than to be enthusiastically for a Mondale presidency.

Even with regard to the one thing my friend and I never got around to: the Supreme Court. Four or five more Reagan appointments to the court could constitute a disaster lasting well into the 21st century. And even that translates into nothing more than another reason for voting against Reagan.