WHY ARE YOUNG people supporting Ronald Reagan in large numbers this year even when many college students disagree with him on issues ranging from abortion to Central America?

One reason is his success in exploiting a strong desire on the part of today's youth for control, authority and clarity. My generation hungers for some system to believe in. We have been confronted by general confusion over the nation's ideals. It is natural that we look for guidance from a value system that is coherent and believable.

President Reagan, who has built a campaign around a return to clear and simple values, offers such a value system, simplistic though it may be. He espouses values many young people want to believe in: economic progress, good jobs, America's rightness abroad.

But why, people ask, don't students adopt the world view of a Walter Mondale? Partly because of his ties to Jimmy Carter, a president today's students remember as extremely ineffective precisely because he lacked Reagan's simple view. Carter stressed the complexity of the U.S. economy and of global politics.

But more of Mondale's problems may stem from conflicts among students themselves. One student told me he was "rebelling against the negativism" of campus liberals; another student said she wanted a "rest from the protests and confusion" of the 1960s and early '70s.

I think some in my generation resent the "big picture" questions raised by the protests of earlier students. Our world, students seem to be saying, is confusing enough without having to grapple with the morality of America's role in every country around the globe. We can, however, seek to control our own careers. And perhaps we can be confident that a good job will bring a measure of acceptance and happiness. President Reagan, by emphasizing traditional values like "getting ahead" and making money, has re- established basic guideposts and made life a little simpler.

Other students I have met plan to vote for Reagan, even though they disagree with him on important issues, because the experience of the last few years has convinced them that a president really cannot affect their lives all that much. Reagan, students reason, is at least a pleasant leader; so why vote for Mondale if he won't be able to do anything better?

If this attitude is difficult to comprehend, pretend for a moment that you are a college student casually familiar with political events since your birth. Review a digest of recent presidential history:

Jack Kennedy, your parents and teachers have told you, inspired people and tried to do great things. He was shot.

In 1964, Lyndon Johnson ran on a peace platform telling the people his opponent would endanger American lives. Johnson got in office and escalated the Vietnam war, resulting in the loss of thousands of American lives.

Richard Nixon, like him or not, seemed to get a lot of things done (principally in foreign policy). He was thrown out of office for breaking the rules. His successor, Gerald Ford, appeared to do nothing.

In 1976, Jimmy Carter was elected, but no one would listen to him. He seemed always to change his mind on what he wanted to do, and when he did make a decision, he couldn't get it done.

This brings the casual student of history to Ronald Reagan, who was elected to shrink the deficit and get the government out of people's hair. Now the deficit has tripled and the president wants to further regulate alcohol, restrict the use of contraceptives and ban abortions.

So Reagan appears as just another politician, albeit one with an alluring image. He is called the most powerful man in the world but abortions are still legal, as they have been since today's students reached puberty, and I have never met a college student who couldn't get a drink. The message is simple: Presidents usually don't do what they say, and when they try to do what they say, they often don't succeed.

This perception that presidents can't make a difference is a powerful force to reckon with. Combined with a craving for simple answers and leaders who offer national goals only in black and white, it has trivialized the vote and encouraged many college students, as well as most of the rest of the country, to decide elections on a whim, an image and a nice slogan.