Whenever Rep. Jack Kemp (R-N.Y.) sees young people in the audience as he goes around the country this fall campaigning for the GOP ticket, he greets them as "my fellow racial, revoluntary young Republicans back there," and then proceeds to give them the hard sell on his "radical" idea: supply-side economics. He also preaches that the Republican Party is the party of opportunity, idealism, compassion and the American Dream.

Kemp, like most other Republicans on the campaign trial, encounters college students and other young people frequently because the Republicans everwhere are making an effort to get as many of them as they can out to party activities. And for good reason. Four years ago, Ronald Reagan ran poorest among the young; one major national poll showed him as the presidential choice of only 11 percent of voters aged 18 to 25.

This year, however, he is strongest with the young. Nearly every national poll gives the president an astonishing lead of nearly 2 to 1 over Walter Mondale as the presidential choice of voters under 25.

These numbers could be ominous for Democrats. The 1984 election is not likely to be a realignment one in which the Republicans become the majority party. But the political preferences of the young have obvious implications for the future. For although the young are often the most volatile voting group, most Americans in the past have continued to vote the way they did the first time they cast their ballots.

Many whose views of young people were set by the generation and activism of the 1960s and early '70s and are accustomed to the young being political liberals can't understand their current turn to Reagan. They see the under-25 generation as the selfish and unworth followers of the so-called "Baby Boom" generation of the '60s, their elders in the 25-to-45 age bracket. This is unfair and inaccurate.

There's no question that a major appeal of the Republicans to the young is the promise of economic opportunity. Comparing the Republicans' approach to the Democrats' is instructive, however.

Last Tuesday, the Democrats held a "Yuppies" Day, in which 30 Democratic House members spoke to rallies and meetings of young people all around the country. It was a typical programmatic liberal agenda -- its prospectus promised discussions of "Reagan's cut of 2 million students from the guaranteed loan and other student aid programs, the president's failure to support Title IX civil rights protection for women athletes and his overall failure to support equal opportunity and education programs."

Reagan and the Republicans, on the other hand, have been offering optimism and patriotism. "Our purpose is not to confer happiness by government, it's to create the climate in which people can work it out for themselves," Kemp says. It's a message that the young people in his audiences respond to. "We're not looking for handouts, we're looking for the chance to work into something that is a long-term opportunity," said a woman student at the University of Minnesota at Duluth.

The 1960s also nurtured the idea that the young are by nature alienated. This may be true of some, but by no means all. "Reagan makes me feel good about my country and its beliefs and values," a North Dakota State student said last week. "I'm tired of negativism and cynicism."

There is a widespread inclination to view the "baby boom" generation as the norm against which other generations of the young are measured. In fact, it was something of an aberration of historical circumstances and demographics. Those who followed it are much more the norm.

The "Baby Boomers" are the largest generation in our history. They constitute almost 50 percent of the electorate today. They were born into a time of unprecedented U.S. global power and booming prosperity, and as a result they took prosperity and personal opportunity for granted as no other group their age before or since.

This contributed to their idealism and had a bearing on their strong disillusionment with the imperfections in American society, their participation in the civil rights movement and then their opposition to the Vietnam War. The strains of that war ended the unbroken prosperity with the usual result -- people became more cautious and conservative.

Frederick Lewis Allen, author of "Only Yesterday," a brilliant social history of the 1920s, saw this same phenomenon in his equally valuable but less famous history of the 1930s, "Since Yesterday." The economic pressures and hardships of the Great Depression, he wrote, rolled back much of the cultural and sexual revolution of the 1920.

Young people today are not more and no less idealistic than any before them, but their attitudes, like everyone else's, are shaped by their circumstances.

The Democrats became the majority party by being the party of hope and opportunity and the young.Their ability to regain and maintain this position will be a key in determining whether they or the Republicans are the dominant party of the future.