Why is the elephant talking like a donkey and vice versa?

This is about that time in the election process when the candidates begin to talk about ''broadening their constituency.'' Which means the Democrats start sounding more like Republicans, and the Republicans start sounding more like Democrats. The President is being nicer to social security - and even to the Russians. Mr. Mondale can be counted on at any moment to say a good word for bankers in return.

The labor unions will understand what Mr. Mondale is doing and forgive him - just as surely as the Rev. Jerry Falwell will not switch his vote to Geraldine Ferraro on the grounds that Mr. Reagan has gone soft on communism.

The ritual is known as ''courting the crossover vote.'' It is assumed that a certain number of Democrats must vote Republican - as they did in 1980 - if Mr. Reagan is to be reelected, and a certain number of Republicans must vote Democratic if Mr. Mondale is to win. And so we have the interesting spectacle of Mr. Reagan presenting himself as the environmentalist's best friend, while Geraldine Ferraro keeps insisting that she is not as liberal as Mr. Reagan and Mr. Bush say she is.

By election time it may be impossible to distinguish the Republicans from the Democrats as both parties not only move toward the center but poach across the enemy line.

Should this make voters as cynical as a political cartoonist dashing off still another sketch entitled ''Politics makes strange bedfellows''?

We think not. In fact, we would like to put in a good word for political role-swapping. Consider: As they pay lip service to fiscal prudence, the Democrats may actually come to appreciate the argument for limiting federal spending. By the same token, as the present administration tries to shed its reputation for being ''trigger happy,'' the peace suddenly being endorsed by Reagan speechwriters may become a genuine value of the heart.

Perhaps we fantasize. But every speaker is also a member of his own audience. One does, to a certain degree, become what one hears oneself reading.

In any case, it is part of everybody's education to understand the opposition.

We are not in favor of hypocrisy.

We are not apologizing for the wishy-washy.

But the pluralism expressed by the two-party system is also present within every individual, and, whatever the ulterior motives, it can do no harm for the one side of us to honor the other side, facing up to the complexities of the heart.

There can be few Democrats who do not secretly prefer at least one plank of the Republican platform to a corresponding plank in their own. And vice versa.

Something in most of us yearns to be both liberal and conservative.

Our instincts tell us that a fanatic is more of a danger to democracy than a waffler.

In ''The Man Without Qualities,'' the Austrian novelist Robert Musil suggests that there may be a second voice even within the fanatic, whispering a tiny no, or at least a maybe. He writes: ''Do you believe that anyone today fighting for or against some cause or other, if by some miracle he were tomorrow made the all-powerful ruler of the world, would that same day do what he has been demanding all his life long? I am convinced he would put it off for a few days.''

In a world where agitated fingers hover above nuclear buttons, a little indecisiveness - a little broadening of one's constituency - cannot be totally bad.