That genial and very perceptive columnist and commentator, Mark Shields, was just the right person to bring up a very delicate subject: the evidence that the Republican Party, in presidential voting, usually picks up most of the white vote, very much to the Democratic candidate's disadvantage.
Mr. Shields cites statistics that indicate this trend has been strong for more than a generation and, particularly so, during the last four elections, when, he writes, the Democratic nominee has won an average of 38 percent of the white vote although the electorate is 89 percent white.
Shields's conclusion is that unless the Democrats begin to start to appeal more to white voters, they may find it nearly impossible to win the presidency.
This is not some GOP partisan talking. Shields, one of Edmund Muskie's right-hand men during his presidential nomination drive in 1972, would probably concede that his private leanings remain Democratic, although his columns show an independent, unpredictable bent.
Shields points out that only twice in the past 40 years - Franklin D. Roosevelt in 1944 and Lyndon B. Johnson in 1964 - has a Democratic presidential candidate won a majority of white votes.
At a time when a nearly bloc vote by blacks is promised Walter Mondale, and whites are flocking behind Ronald Reagan, Shields's assessment of the effect of this trend is relevant and welcome. No one likes to mention how much race still enters into the US political scene.
The ''race issue,'' as used here, is for the most part a reference to a pro-white and pro-black attitude, as opposed to an antiblack and antiwhite point of view.
That is, both whites and blacks in recent years have been voting more in what they perceive to be self-interest than in opposition or even hatred of each other.
Underscoring the rise of blacks in his new book, ''The Good News Is the Bad News Is Wrong,'' political analyst Ben J. Wattenberg points out that among many other gains, the blacks in college numbered 1,227,000 in 1982, as opposed to 227 ,000 in 1960. He adds that during the late 1970s ''a milestone was passed,'' with more blacks working in white-collar jobs than in blue-collar jobs.
Mr. Wattenberg writes that the ''central fact known to all is the blacks are still well behind whites in America. But behind that fact,'' he adds, ''are some stunning successes and some catching up that is so startling as to have been unimaginable 20 or 10 years ago.''
It is against this trend of relative black progress and relatively better black-white relations, however, that evidence of a growing, if temporary, polarization of the races is being noted in this presidential election, particularly in the South. Reporters and pollsters are reporting that the Democratic get-out-the-black-vote drive in the South, led by the Rev. Jesse Jackson, has brought about a backlash of increased white registration.
What adds to the polarization is the decision by the President and his political advisers to pretty much write off the black vote.
Most blacks feel that the President supports an economic approach that does not reach down to assist them. Further, they feel that he has been mainly responsible for cutting into social programs that they depend upon. Mr. Reagan denies this, but Mr. Mondale tends to harden this perception whenever he speaks about Reaganomics.
Reagan insists he is helping all of the poor, including the blacks, who fall preponderantly in that category. He says that reduced inflation aids the poor and that also, of late, there has been reduced unemployment in their ranks. Black leaders call Reagan's approach a ''trickle-down'' that never quite trickles down to the disadvantaged. And they cite the figures of continuing, extremely high joblessness among black youth.
But whatever the merits of that argument, there is little evidence that the melting-pot theory is working very well on the political scene as far as blacks and whites are concerned. The heated feeling between the two races has decidedly lessened since the '60s. But there is this tendency for blacks to vote Democratic and whites to vote Republican - and the division it clearly exemplifies.