Imagine this scenario, if you can: Senate minority leader Bob Dole is speaking at a rally in South Carolina. There isn't a black or brown face in the crowd. The presidential hopeful from Kansas tells the all-white group he intends to change the Republican Party's ''image of insensitivity to black, brown, poor-white and disabled Americans.''

Is Bob Dole off his political rocker?

No. Dole knows that the only way he can overtake Vice President George Bush and get the Republican nomination next year is to portray Bush as the elitist, country-club candidate and try to sell himself as the man who cares about people who need food stamps, medicine for their afflictions, help against bigotry.

Now, that's a ploy that would work if Dole were contesting Ronald Reagan, but he's going to have trouble selling people the argument that Bush is a heartless, fat-cat basher of America's down-and-out people. That is a bum rap against Bush that even black Republicans will not swallow.

But the ''I'm-for-the-little-guy'' campaign is Dole's only hope of overtaking Bush, whose front-runner status always has been suspect.

Dole's appeal to blacks, Hispanics, the underclass has implications for next year's presidential campaign itself, should he, by some great political stroke, win the GOP nomination.

With luck, personal charm, a lot of misstatements and the privilege of running against weak Democrats, Ronald Reagan proved he could snub blacks, cheat the poor and still win by a landslide. Dole knows that whoever wins the GOP nomination next year cannot win by alienating these groups of Americans. Neither Dole nor Bush can pull off a Hollywood con job.

Asked why he was urging the inclusion of blacks while speaking only to South Carolina whites, Dole said: ''Because it is the right thing to do, and because votes are the name of the game.''

Dole surely knows that Reagan has bequeathed to the 1988 GOP nominee a host of grim problems and embarrassments, including the Iran-contra mess, record budget deficits, a possible Persian Gulf debacle, a Central American nightmare, a U.S. foreign-trade mess. Dole knows the conventional wisdom is that 1988 is supposed to produce a Democratic president.

But the shrewd Kansan sees that the Democratic Party is still in disarray. It has no ''white knight'' who shows signs he can ride into the nation's capital and take charge.

It does, however, have a "black knight" by the name of Jesse Jackson. I'll wager that Dole has looked down the road to see Jackson winning a lot of southern convention delegates on ''Super Tuesday,'' March 8, and then a bit farther to see the Democratic National Convention refusing to consider Jackson seriously, partly because of his blackness, but even more on grounds he is ''too liberal.'' That's when Dole's pulse must quicken at the thought of angry blacks abandoning their party and voting for him.

I read of Bob Dole pursuing his ''southern strategy'' and become all the more convinced that I am right in saying that George Bush isn't even close to locking up the Republican nomination.

The Democrats could become shocking losers in the 1988 presidential contest.