There is something about politics that reminds me of the blue-plate special. You have to take it all or you take none of it. The rule in politics as in all cheap restaurants is always the same -- no substitutions.

What brings this up at the moment is the sense I have that people would like to have a tax cut and some of what is always called fiscal restraint, a dip in inflation and maybe some more missiles in the old national gun belt, but if it's all right with you, we do not ask for Alexander Haig.

I'm sure this is the way some people felt when the Democrats ruled the land. They voted for the economic program, and they got stuff like busing. They voted for a man, and they got a brand of liberalism they didn't particularly like. They voted for simple matters like Social Security, and they got a government welfare program they found personally obnoxious.

Now the Reagan administration seems about to do the same thing. In Haig, they are considering a man who built his career in the twin debacles of Vietnam and Watergate and has come out of it -- Howard Baker, knock on wood -- technically clean. It means nothing. In both, Haig developed and implemented policy. In both, he is tied by his own actions to the bombing of North Vietnam, the continuation of the war, the tapping of telephones here, the defense of Richard Nixon and, finally, his pardon for crimes that Haig himself was too obtuse to discern when he worked for the man.

What matters is not whether Alexander Haig has been politically agile, has managed by inches and through bank shots and by terrific skating over the thinnest of ice, to remain officially and certifiably pure, but whether he has the capacity to make moral judgments -- to recognize what nearly the entire country came to know about Watergate and what kids in the street knew about Vietnam.

Maybe it's a matter of age. The Reagan administration may be too old to know that. The president-elect is 69 and will be 70 when he is inaugurated. The men we are told are closest to him are either his age or older. In one sense this is to be welcomed. For too long, the presidency has been talked about as if it were a position on a football team -- left presidency, or something like that. The premium has been put on energy, on physical stamina -- on the ability to put in punishing hours and travel around the world at the drop of the hat. No one talked much about wisdom.

But Ronald Reagan and the men around him are too old now and were too old then to appreciate what the Vietnam War meant to a whole generation of Americans. Reagan himself has time and time again shown that he has never gotten the point, never really understood the reluctance of young men to die in the 1960s for the anitcommunist orthodoxy of the 1950s -- the one that prompted Reagan to call Vietnam a noble war.

It is the same with Watergate. It, too, was a rite of passage, although not exactly a generational one. Watergate was not about partisan politics. It was not even about politics. It was about honesty and trust and it came because Vietnam and a whole lot of other things had convinced many people that the one thing the government has to do -- always and under all circumstances -- is tell the truth. Everything after that is superfluous.

Certainly the consideration of Haig is not only a reflection of age. The lessons of Vietnam and Watergate were not lost on plenty of older people, some of whom in fact were the first to point them out. But to a whole younger generation, these lessons were inescapable. Nothing sharpens thinking as much as the prospect of military service, and nothing is as tragically absurd as one generation being asked to fight for the discredited ideology of a previous generation.

Al Haig represents all of that. In his case, Vietnam and Watergate are not events but symbols of a mentality that cost young men their lives and a government the confidence of its people. He represents the old way, the way it used to be, the way a whole lot of people worked very hard to change -- sometimes in the streets, sometimes at the ballot box. You don't have to be old to like Al Haig. It's just hard to believe you could have ever been young.

Can we substitute?