The trouble with Yuppies is that they don't always behave the way they are supposed to. Or the way Gary Hart expects them to. That's what makes today's Democratic presidential primary in Connecticut so fascinating to watch.
Yuppies, as many people know by now, are the latest trendy happening in American politics. The name stands for ''young, upwardly mobile professionals.'' These are the cream of the baby-boom generation - the well-fed, well-clothed, well-housed, well-educated children born during the 20 years after World War II (1946-65).
Yuppies are not all rich; but they are all headed in that direction. They are sometimes derided by non-Yuppies as ''the Volvo-and-brie set.''
Yuppies gained notoriety after the New Hampshire primary. Experts who analyzed the election returns discovered that Yuppie-type voters had been instrumental in Senator Hart's last-minute, come-from-behind victory.
Since that time, it's the Yuppies who have voted most solidly for Hart in Massachusetts, Florida, and several other states. It's the Yuppies who spread the word about Hart and who get most excited about the idea of a Hart White House.
As a rule, Yuppies eschew party politics - Democrat or Republican. They are ''independent,'' drive foreign cars, went to good schools, make more than $30, 000 a year, and usually live in the suburbs. A large proportion of them are ''computer literate.'' Many belong to two-income families. For the first time, a lot of Yuppies are moving into positions of authority as they reach their mid-30 s.
That brings us to today's primary in Connecticut. The Nutmeg State is loaded with Yuppies - the young, up-and-coming bankers from New Canaan, the corporate lawyers from Greenwich, the architects from Westport. Connecticut's Yuppies take the train every day into New York City, or hop a commuter bus into Hartford.
If all goes as expected, many Yuppies will step off the train this evening in places like Darien and New Canaan, get into their Mercedes sedans, and go to vote for Hart.
This is one reason the Hart team has high hopes in Connecticut. The state, you see, is considered Yuppieland, the heart of Hart country.
Recently, however, there have been some disturbing trends among the Yuppies, at least from the Hart viewpoint. In Illinois, where Hart was counting on them to give him a victory, the Yuppie vote split almost evenly between Hart and Walter Mondale.
This threw Hart's planners for a loop. And it served as a warning that Yuppies are not to be taken for granted. Just because they voted 2 to 1 for Hart in one state does not guarantee they will do it again.
Why do Yuppies like Hart? And what kind of issues motivate them?
Dottie Lynch, the Hart pollster, says younger voters are drawn to the senator's promise of ''new ideas'' and ''a new generation of leadership.'' They like the comparisons that are drawn between Hart and John F. Kennedy. And they appreciate Hart's qualities of independence.
ABC-TV exit polls among thousands of voters in this year's primaries tell us more about what Yuppies like.
The most important characteristic they are seeking, the polls show, is a person who will bring change to Washington. They also want someone who will ''get things done.''
''Experience,'' which is Mondale's watchword, rates far lower on the Yuppie scale of values.
Among the issues, Yuppies are most concerned about wasteful government and war. They want the next president to hold down spending, cut red tape, and reduce the threat of a nuclear conflict.
At the same time, they are not very worked up about the problems of the poor and elderly, or about unemployment - two issues that unite Mondale voters.
Yuppies think Mr. Mondale makes too many promises to get votes, and they admire Hart's ''clear, new ideas.''
A lot of Yuppies consider themselves ''liberal,'' but most of them, in their apolitical fashion, put themselves down as ''somewhere in between liberal and conservative.''
Two or three final thoughts on Yuppies and today's vote:
In Illinois, the Hart-Mondale battle focused mostly on the senator's ''mistakes'' - especially one of his advertisements criticizing a Chicago political leader. Hart never got a chance to sell his message about new ideas. As a result, many Yuppies voted for Mondale, and others just stayed home. The turnout among young voters in the suburbs was unexpectedly low.
In Connecticut, no one knows for sure what will happen. The polls show Hart ahead - but they showed him ahead in Illinois until the last moment. Telephone canvassers in Connecticut say things are more unsettled than the polls indicate. They say a lot of voters are lukewarm toward both the leading candidates, and could go either way.
A further worrisome note for Hart. In West Hartford, one of the favorite roosting places for Yuppies, canvassers say there's been a shift since Illinois toward Mondale.
What does that mean? No one's quite sure. But political analysts note that Yuppies were raised on a heavy diet of TV. They say most Yuppies, if they got bored with Hart, wouldn't hesitate to change channels.