The mark of the liberal, as with the psychotic, is the compulsion to work against his own self-interest. This accounts for the willingness of affluent liberals to support the progressive income tax and helps explain why someone like me, who has just enrolled his one and only child in a private school, thinks that the proposed educational tax credit is the contemporary version of "Let them eat cake." It may or may not work for everyone, but it will certainly work and work well for the rich.

Like the estate tax, the effort to reform the sex laws and some other measures, I am not sure where in the world this tax credit thing has come from. I never heard of it, don't remember seeing it on the ballot, read nothing about it until last week and now am confronted with a citizens' committee for it, one against it, and the usual conflict between my purse and my conscience. On this one, the conscience wins hands down.

The proposal is in the form of an initiative and will be on the November ballot. It would permit District residents to write off as much as $1,200 for each child enrolled in either private or public schools and it could cost the city as much as $40 million in tax revenues. It has been denounced as unconstitutional, racist, a death blow to the public schools, all of the above or none of the above. What it is, in a sense, is an idea whose time has come.

This is not to say that it is a good idea. It is merely to say that it is timely, that it represents the sort of thinking that is overtaking this country. What is proposed as a boon to the school system, is really nothing more than an appeal to selfishness in which the poor, the weak, the handicapped, the under-educated and the just plain unlucky are being cut loose. Unspoken in all this is a kind of fatigue -- a weariness with high taxes that seem to accomplish little, with a school system that can't seem to do its job, with money being spent and little to show for it.

Tax credits, after all, mean nothing to the poor. Cash means everything to them. If you have no money, you cannot spend it and wait until the end of the year when you get a rebate on your taxes or pay less to the government in the first place. All this is the bookkeeping of the rich, of people with money.

From the standpoint of what it would do to the city and its finances, the tax credit is a bad idea. It would cost the District lots of money. From the standpoint of the schools, it may or may not be the coup de grace to the system that some say it is -- despite its vaunted transferability provision. It certainly will do it no good. In theory, parents of public school children also will be able to take a tax credit for their expenses. So, in theory, they might wind up contributing so much more for teacher aides and crayons and reading materials that the city's schools will actually bloom and people from all over the United States will kill to have their kids attend school in Washington. There is a much greater chance, though, that the initiative simply will further deprive the city of revenues with which to run that very school system.

There is, however, yet another reason why the tax credit proposal is foul and it has to do with the matter of equity. This is not a matter of liberalism or conservatism or even a debate over private versus public schools. lWhat is so obnoxious about this proposal is that it goes to the heart of the notion of community: what we owe others. There is a notion as old as the Bible, as old as the concept that the strong have an obligation to the weak, the educated for the uneducated, the rich for the poor. It is Christian. It is Jewish. It is Muslim. It is, for crying out loud, basic.

But here we have a proposal that says just the opposite. It says that you can take out of the public school system or the city some of what you opt to put into private schooling. It says that you can turn your back on your obligation to the people who don't have the option of private schooling, make their schools in some measure worse, make yours better, and have them pay for it.

This goes to the heart of the notion of community and it also goes to the heart of the notion of liberalism. The liberal really is not someone who does not understand his own self-interest. Instead, he is someone who recognizes that his self-interest cannot be separated from the interest of his community.