For the first time, the Reagan administration has been forced to admit, in the new budget message, that the yawning gap between federal revenues and federal spending cannot be closed by an economic recovery of even large dimensions.

And although it is not explicitly stated, officials admit privately that the budget can't be balanced, either, by further large cuts in social spending: the grim realities of the declines in the "smokestack industries" promise high unemployment, with all its cost consequences, well into the future.

To be sure, President Reagan doesn't enter a plea of guilty. He doesn't even admit that his recognition of these realities comes late.

Instead, the new budget document offers a tortured analysis that blames the sickness of the economy entirely on the failures of his predecessors. Forgotten is the assurance in last year's budget message that the recession--a mild one --would be over and done with before the end of 1982.

Only 12 months ago, Reagan was bragging that he had made "dramatic progress in reordering fiscal policy" with a similar "redirection" of monetary policy.

"In short," he said then, ". . . a solid foundation has been laid for a sound dollar, sustained real economic growth, lasting financial stability, and noninflationary prosperity for all Americans."

So what happened? How did Reagan manage to run up a budget deficit of $208 billion this year, instead of the $91.5 billion he forecast last year? Why is the federal spending ratio at a staggering 25.2 percent, instead of falling to 22 percent, as he promised last year? He now predicts a $315 billion deficit in 1988 "even under assumed economic conditions of full employment in 1988." (Full employment is defined as 61/4 percent unemployment).

According to the new budget document, the administration has just now discovered that about two-thirds, or $140 billion of the 1983 deficit is "structural" and represents the long-developing policy imbalance that was embodied in the 1981 budget inherited by the present administration."

How come this inherited "structural" deficit wasn't discovered somewhat earlier? His lame answer: "The accumulated weaknesses and imbalances in the U.S. economy proved to be far greater than understood by those inside or outside the government in 1980. The process of correcting the damage . . . therefore has proved to be far more prolonged and disruptive than anticipated."

The real answer is that Reaganomics was a non-starter, as OMB Director David Stockman confessed as far back as 1981, and all of the government's economic projections in both 1981 and 1982 were horribly wrong. Now, the Reagan team admits, the U.S. economy at the end of this year will be smaller by the staggering sum of $550 billion than they thought when they took office.

That means that over time, tax revenues will be $150 billion a year less than anticipated. And to finance swelling deficits at double-digit interest rates, the annual cost of servicing the national debt this year will be $128 billion and is estimated to rise to $179 billion in fiscal 1986.

"So we've got about $50 billion a year in permanent (additional) debt-service costs built into these out-year budgets now, because of the two-year correction, getting this inflation out of the economy that we've gone through," says a senior administration official.

Two-year correction? Getting inflation out of the economy? "Disinflationary correction," as we find it put in yet another euphemism for a disastrous recession?

Let's put it in English: the economy is in this box because of the Reagan administration's terrible miscalculations in 1981. The president set in motion an enormous tax-cutting program, a massive boost in defense spending, and encouraged the Federal Reserve to slam on the monetary brakes. This was the "riverboat gamble" that Howard Baker talked about, "voodoo economics" as George Bush labeled it. Having been convinced by Secretary of State George Shultz and others that something has to be done about the deficits he created, the president now has been sold another bad idea, an "insurance program"--the standby surtax tax measure--to add revenue back into the equation. Why put a new surtax on the books at the very time a tax reduction would be going into effect through the indexation system?

Happily, Congress seems to be drawing the right conclusions. The standby idea, as well as foolish penny-ante savings (such as those proposed for food stamps and certain old-age benefits) will be rejected. What is needed is a sensible slowdown in the growth of the defense budget, and real tax increases--including an attack on tax loopholes--beginning next year.