For nearly the whole 100 minutes of Sunday night's debate I felt eerily invisible. It wasn't that I didn't care about such issues as balancing the national budget, taxes and social security. After all I am an American. What was missing was any recognition of my existence as a black American.

No, that's not quite right. Walter Mondale did seem to be aware of my existence. But he seemed to take special pains not to be caught actually mentioning it. Instead he winked at blacks with his talk about fairness, poverty and a mention or two of civil rights, clearly hoping that we would understand that he was still our friend but understand also why he couldn't afford to say so out loud. Not politic, you know.

And the unsettling thing is that I did understand. I understood that the plight of black Americans, which used to be up front in the nation's consciousness, has become a sort of tasteless subject not to be mentioned in polite company. I understood why Mondale didn't acknowledge my existence. I understood what our new invisibility says about the mood of the country.

Later I found a lot of black people shared my reaction -- not so much raging anger as a low hum of chagrin.

They understood, as I do, why white America doesn't want to think about us right now. America's mood today is paradoxical -- feeling at once threatened and elated. Blacks, immigrants and the poor are seen as pressing, encroaching. And the country is savoring the sweet taste of recovery, albeit grossly uneven and perhaps fleeting.

But what kind of statement is made to blacks about their country when their presence in conversation becomes an embarrassment? In social terms, this would be like pretending a person who is very much present is not there -- in short, invisible.

The invisibility leads to a growing realization that the mood of the country eventually will be translated into public policy.

The mood of the country that has brought us to this place has been developing for several years now. That's why blacks rallied with so much enthusiasm around Jesse Jackson. He put their issues on the nation's agenda and stood as a symbol of visibility. And if his subsequent treatment reinforced black unimportance, the debate drove another little nail into the coffin.

No, "coffin" is too strong a word. Blacks are far from being totally dead in the national consciousness. But when Mondale can so blatantly take the seven to nine million votes he may get from blacks for granted, blacks sense the depths of their problem. As one friend of mine put it: "We're left to rely on the feeling that Mondale, no matter what he's doing in the election, will come out on the right side. We're the throwaway gamble -- everything is tossed into the pot but the returns are deeply in doubt." But if the debate presages the agenda of either candidate once they are in the White House, blacks won't be in on the play, they'll end up sitting on the far end of the bench.

Blacks feel uneasy about this new mood in America, but don't know what to do about it. They wonder to what degree the new centrist approach locks them out. They have stuck with the old Democratic coalition at a time when many blue-collar workers and Jews have left it. They're feeling increasingly that there must be some black realignment, as has occurred with other traditional Democrats, feeling that they may have to become independents or Republicans when it is in their best interest.

I understand that some people will feel that I'm making too much of a distance between Americans and black Americans. But we're not yet at that point when "American" and "black" are synonymous. This is no wish to further fragment America, but a bow to the reality of a growing unease I'm sensing among blacks, the low hum of rage I'm hearing.

Webster defines humming as "singing with the lips closed." I hope that during the coming debates, the hum is not escalateld to a moan."