Almost nobody has a good word for economists any more, including economists. Taking note of the disarray in the profession, presidential aide Ed Meese, discussing some of the excessively optimistic projections made for President Reagan a year ago, revived a Reagan one-liner at a recent Washington Post lunch.

"An economist," he said, "is a fellow who has a Phi Beta Kappa key at one end of his watch chain--but no watch at the other."

It's an old complaint. After receiving so much economic advice beginning, "on the one hand--but on the other hand," President Truman expressed the wish for "a one-handed economist." Jimmy Carter, frustrated by a ballooning deficit and an inability to control inflation, was heard to mutter that he knew a mystic in a little town of Georgia who could see the future better than did his economic advisers.

All of this, of course, is largely unfair, because presidential economists are rarely allowed to act as economic advisers, but are forced, often against their will, to blend in some political judgments. If they don't, presidents will do it for them.

Charles L. Schultze, who survived four years of Carternomics, told the annual economists' conclave in Washington over Christmas: "The economist turned policy adviser will quickly discover that in the councils where economic advice is formulated, one-half to two-thirds of the discussion has little to do with economics, at least in the conventionally defined sense."

When Gardner Ackley and the late Arthur M. Okun warned Lyndon Johnson that he couldn't have guns and butter without causing inflation, LBJ went ahead anyway, conspiring with his defense secretary, Robert S. McNamara, to hide from Ackley, Okun, and Treasury Secretary Joe Fowler the real extent of his proposed military buildup in Vietnam.

Herbert Stein, who was Nixon's chief economic adviser, makes the point that presidents tend to become their own chief economists. In an article in The Conference Board's magazine, he tells of a conversation he had with Nixon in the spring of 1973 when Nixon was considering restoring a wage-price freeze like the one he imposed in the summer of 1971:

"I said, quoting Heraclitus," Stein writes, "that you cannot step into the same river twice. He replied that you could if it was frozen. . . . The decision went his way--a freeze was restored. And the outcome went my way--the new freeze was an instant flop. That experience tells something about advising, also."

At the beginning of the Reagan administration, we learn from David Stockman's confessions in The Atlantic Monthly, the president's economists knew full well that they couldn't cut taxes, increase real economic growth, lower inflation and interest rates, send defense outlays to new highs, and balance the budget by fiscal 1984.

But that's what Reagan wanted. So his economists juggled computer inputs, and provided him with what Treasury Secretary Donald Regan called their "rosy scenario," setting out a real growth of 4 percent for 1981. (Actually, the more rabid supply-siders would have gone even wilder if Economic Council Chairman Murray Weidenbaum hadn't injected a small note of sanity.) But even as modified, the "rosy scenario" had to ignore the recessionary impact of the high interest rates implied by a tight Federal Reserve policy.

Now President Reagan, anxious to maintain his "supply-side" theory (and to avoid admitting that he made a mistake last year) is pressing his economic advisers to read excessive optimism into the figures once again.

If the president ignores the forecasts by his own Office of Management and Budget and by the Congressional Budget Office, which show huge deficits ahead, it will do more than raise new questions of his credibility. Inevitably, it will raise the question of whether there is any role at all for professional economic advice in the government.

John P. Lewis, a member of President Kennedy's Economic Council, once put it as well as anybody: "You can't be a white-smocked scientist here. You have to share the objectives of the administration. But you also have to say your piece --say it inside--and if your point of view seems too far at odds with the boss, you can quit." Some day, some high- ranking economist in some administration will quit on a question of principle, and that may help to lift the present low state of self-esteem in the profession.