A good critic represents a kind of public conscience. As such, he can, and should, express himself on the wisdom of major projects before they are built, and on the quality of them after they go up. Under the best of circumstances, if his arguments are consistent and cogent, his ideas will begin to affect the planning of buildings, and he will thus have a long-term effect on the shaping of ideas and taste. But that is not the same thing as damning a new building and then watching it disappear the next day, like a play that has been panned.

So why did Donald Trump think that Paul Gapp's harsh words had put an end to his dream of building the world's tallest skyscraper? Is this suit a case of journalistic harassment, a demand for censorship, that is likely to have a chilling effect on criticism in general?

If Mr. Trump wins, it could well make legitimate criticism more difficult. But the likelihood is that Mr. Trump has a hidden agenda in this suit, and that it has little to do with censorship or even with libel. He knows, after all, that his world's-tallest-building project faces enormous economic and political hurdles, including opposition from another developer who believes that the city has already given him the right to build on the landfill site Mr. Trump has selected.

This building has never been a certain bet, in other words. But Mr. Trump, realizing this, may well have felt that he had nothing to lose, and a lot of publicity to gain. By filing the suit he has, first of all, identified himself more firmly than ever before in the public's mind as the developer of this particular site, and as the man who intends to build the world's tallest building.

And he has also identified himself as a developer who stands up for New York, and that cannot hurt his reputation. For Mr. Gapp's column did bespeak some unhappiness that a New York building might overtake Chicago's Sears Tower as the world's tallest, and Mr. Trump, local boy that he is, seized on this, knowing that he might also claim simply to be fighting that Chicago chauvinism that is trying to prevent New York from having what is rightfully its own.

There is one wrinkle to all of this, however. Mr. Trump's legal complaint refers to the illustration that accompanied Mr. Gapp's column as an ''atrocious, ugly monstrosity,'' which seems like an odd thing for a developer to call his own building. It turns out, however, that the drawing that The Chicago Tribune published was not provided by Mr. Trump, who claims that the building is not even designed yet. The drawing was created by the Tribune itself as its guess at what the Trump building might look like.