Trumpet fanfare, please. On Nov. 27, the Treasury Department announced a tax simplification plan of the type President Reagan has long wanted. The plan made page one in all the newspapers. Television filmed it, lobbyists loathed it, columnists dissected it, the public embraced it, and in his State of the Union speech the president said he was all for it. Ta-da.

But for what? It turns out, as The Wall Street Journal put it, the president was "unaware" that the Treasury plan would raise corporate taxes about 37 percent. When that paper asked him in an interview what he thought about that, the president flinched: What rise? What corporate taxes? Delicately, I imagine, the Journal told him what was in the Treasury plan. The president said he was not pleased.

Throughout America, corporate executives and coupon-clippers alike presumably jumped for joy, hugged their secretaries and called the club, saying they were coming over early. Charls Walker, one of Washington's top business lobbyists, said the president's remarks "made my day." Here they all had naively thought that corporate taxes might increase -- that the president knew, even in a general sort of way, what was contained in the proposal he had pronounced "the finest" and vowed would become law. Silly, silly people.

Of course, it's well known that the president is not a detail man, and the Treasury package was nobody's idea of a final draft. Still, we are not talking mere details here, but the sort of broad policy decisions that moved even Ralph Nader to sing arias of praise for the proposal. The increase in corporate taxes was a basic part of the package. Without it, the Treasury could not claim that individual tax rates could be lowered and the package still remain, in the jargon of the day, "revenue neutral."

Even after more than four years of Ronald Reagan, this is a remarkable episode. With tax simplification, we are not talking about some minor bill, but genuine trumpets -- a major, even epic, piece of legislation. You would think that the president would be familiar with its major provisions, especially since one of them -- an increase in corporate taxes -- amounts to a reversal in policy.

Does any of this matter? Not really, comes back the reply from lots of people. They point out that Reagan is a smashing success as president, and it hardly matters that he concentrates only on the big picture, leaving the details to others. Look at the economy, they say. Look at the inflation rate, they say. Look at the deficit . . . No! No! Don't look at that. But the deficit is exactly where they should look. It is out of control precisely because Reagan looks only at the big picture -- at the result he wants. How you get to that result is, as they used to say, not his dertment. The trouble is that wanting something is not the same as knowing how to get it. The "details" are really building blocks.

It's the same as "Star Wars." Wanting to do away with nuclear weapons is not a technological breakthrough: It's a wish, and no amount of wishing changes the awful logic of deterrence. A tax plan that decreases everyone's taxes and still takes in the same amount of money cannot really exist. Like "Star Wars," it floats above reality like a balloon, and it soars for only one reason: The facts have been thrown overboard.