BOSTON -- The younger generation wants to know what the big deal is. Why is everybody making such a major production out of this tax thing. Hey.

The older generation is taken aback and answers sharply: The president of the United States has broken his pledge! George Bush went back on his promise! He told us to read his lips: No new taxes. Now he says taxes!

The younger generation, of Reagan vintage with a bit of Bush mellowing, says to its elder: Chill out. Nobody thought he meant it. Like, it was just a campaign speech. I mean it was ghostwritten. You can't take that stuff seriously.

The older generation, of Watergate vintage with a hint of Vietnam, says to the younger: We take it seriously when the president of the United States talks. When he pledges allegiance to an idea, it's supposed to mean something.

The younger generation roll their eyes. Well, that's your problem. I mean, do you believe that Grape-Nuts is going to make you feel better, that Oil of Olay is going to make you look younger? That Doublemint chewing gun is gonna double your fun?

The older generation summon up their dignity. The presidency is not an ad agency. Making public policy is not the same as selling detergent.

The younger generation says, succinctly: Get real.

There is a momentary lull over the generation gap, while Middle Age thinks, ''They're so cynical,'' and College Age thinks, ''They're so naive.'' Then it starts up again.

Twentysomething asks sympathetically: Do you, like, take this stuff literally? I mean, don't you get it? It's sort of like ''2 Live Crew.'' It's all words. It's just rap. They don't mean what they're saying.

Fortysomething doesn't answer for a minute, because to tell you the truth they took ''2 Live Crew'' literally. Besides, they are feeling patronized, and middle-aged, the way they feel when the Rolling Stones is playing and someone says, ''Hey, wow, Oldies.''

More to the point, it's beginning to sound like a scene from one of the surveys about ''The Younger Generation,'' that keep appearing in the newspapers that the elder generation reads and the younger doesn't.

In the latest of these polls, the Times-Mirror described 18- to 29-year-olds as a generation that ''knows less, cares less, votes less and is less critical of its leaders and institutions than young people in the past.'' The elders, opposed on principle to youth-bashing, would prefer to throw in another phrase: ''They expect less.''

The older generation raised in the wake of World War II grew up with enough expectations to be disappointed, enough faith to be disillusioned. Faced with the Vietnam draft, they couldn't avoid the connection between private life and government. They were angry when Nixon lied. They listened when Carter said he wouldn't. Without laughing.

The younger generation, raised on the crest of Reaganism, have one-upped their parents' disillusionment with uninterestedness. Heirs to the '80s, they learned from Reagan not to look to government.

So instead of voting, they recycle; instead of looking to politics, they focus on a point of light or two. After all, heroes are to be toppled, and politics is for entertainment. They won't get caught taking it seriously.

The older generation thinks there is an ironic twist to this discussion. In fact, fortysomething believes the president has to raise taxes, but also thinks that leaders should be held accountable. A president who breaks a pledge should have a reason, should explain himself or admit it was all a lie.

Twentysomething doesn't know much about the tax debate, but takes it for granted that politicians lie. Or to put it another way, politicians change their act. Madonna gets a new image every year, so why not George?

The older generation takes a last verbal stab at this impasse. Sounding dangerously ponderous, it says: ''If you accept this, if you don't hold leaders accountable, if you don't believe that what is said matters, then you aren't active citizens but a passive audience.''

The younger generation listens for a minute and then says kindly to its elders, ''Hey guys, lighten up.'' And then it changes the channel.