Coming back to Washington in these September days is a bit like stepping back into Europe in the fall of 1939. The war is on, the early assaults over, the troops deployed, the tanks and planes await orders to attack, but everywhere an eerie lull hangs over the battlefields.

Now, as then, it is the time of "the phony war." Now, as then, everyone knows savage conflict lies ahead.

The only questions are when it will begin and who will be the winner when it's over.

What we're witnessing now in the capital are the inevitable nervous tremors that sweep the ranks before the real combat starts. And something more. All around us are signs of disorder and a sense of defeat approaching panic--and all before the first shots are fired.

How else to explain the frantic attempts to explain away unexpected problems, the unseemly efforts to place the goat's horns on anyone in view, and some far removed from sight and sound?

Not since the viciously wrong-headed arguments over "who lost China" in Harry Truman's day has Washington experienced so phony a political debate as is now under way.

The culprits are also all around us.

To hear the president and his people tell us, Wall Street did it. Or the press did it. Or the big liberal spenders of the past, Democrats naturally, did it. Or even the hapless Jimmy Carter was the one who did it.

(Carter should be flattered. As the original fumble fingers in the White House, this is the first time in memory he's being credited with the ability to influence anything or anyone, anywhere. We'll have to rewrite the book about the guy who couldn't do anything right.)

Scapegoating is an old and accomplished art in Washington, so this present rush to find the criminals responsible for doing in the president's so-called economic recovery program isn't surprising. In politics as in war, offense remains the best defense.

Shooting at such targets doesn't mean you hit them, however; nor, deadly business though this is, that their selection as villains lacks a certain humor.

The idea that Wall Street somehow is to blame for the failure of President Reagan's program to perform as predicted comes as the greatest joke. Hardly any group hungered more for the benefits the Reagan presidency would bring than the brokers of Wall Street, and surely none responded more eagerly to the early efforts of the new administration.

Remember the "Reagan market" that took off like a rocket, soared up and up, crashed through the Dow Jones barrier of 1000 and climbed even higher? That was only a few months ago. Wall Street was then reflecting its heart.

It believed, or wanted to, and reacted accordingly. Wall Street still wants to believe--it is, after all, the preeminent place of dreams, many of which come true--but it lives amid daily hard realities. It also stands as the place of supreme pragmatism. Wall Street needs to be shown.

The worst-kept secret in Washington now stands fully exposed: that the numbers in the Reagan plan don't add up.

That shouldn't come as too great a shock to the public.

You don't have to understand advanced calculus to realize that if you slash taxes to take three-quarters of a trillion dollars out of the federal budget and then plan to put some $1.6 trillion back in defense spending it's going to take a political Houdini to come out with a balanced budget as forecast.

You don't have to be an economist either, whether out of Keynes or Friedman, to wonder if this unproven theory we're now forced to test doesn't pose great and unnecessary risks. That's what many experts from all persuasions and disciplines have been saying for months now.

Before Reagan won his great tax reductions in Congress, an internationally known scholar at MIT's Alfred P. Sloan School of Management studied the president's economic proposals and came to a disquieting conclusion. Prof. Jay W. Forrester's evaluation made these points:

Higher inflation will result from the tax cuts unless the budget is balanced quickly.

Tax reduction gives no supply-side incentive when it adds to the government deficit.

Further budget cuts are the most effective governmental action to provide supply-side vigor in the economy.

Continued budget reductions should not be postponed in the vain hope that tax cuts alone will produce a stronger economy and higher government revenues.

Even tighter monetary policy--and that means high interest rates--is needed to stop inflation and increase production of the private business sector.

Such an analysis was far from unusual. It simply wasn't being taken seriously.

Amid cheers, chortles, and jubilation Congress swept aside all doubts, abdicated its powers to the presidency, and en masse attempted to escape individual responsibility for what was being done by a blanket resolution vote locking in the nation to the great tax cut experiment.

Now suddenly the great experiment appears more dubious.

No less a hard-eyed observer than James R. Schlesinger, who was Richard Nixon's acting budget director as well as his defense and CIA chief, tells readers of this paper that that tax legislation "seems likely to go down in history as the single most irresponsible fiscal action of modern times."

And now, with the Congress back, the political terrain far more rugged, and the prospect for quick, easy victory becoming all the more doubtful, the skirmishing ends and the real war, not the phony one, begins.

In his first eight months as president Ronald Reagan has demonstrated one great trait. He's shown that a politician still can stir the country and, through force of personality and by capitalizing on his popularity, move it in a new direction. People have responded positively to him. They voted for a change, a real change, and, as they have shown so far, are willing to go a long way to give him that chance.

These are the positive sides of his politics of personality and good cheer.

But people also want something more than good will. They've been promised great results many times before, and still are waiting for them to materialize. They want something that works. They especially don't want excuses about how wonderfully the prescribed medicine would have worked if only the bad guys hadn't poisoned it. And all before they took the first swallow. Their patience will wear thin quickly with such tactics. Worse, they will be more disbelieving and less willing to respond to presidential appeals the next time.

Those are the consequences of failure, and failure at this juncture, after what we've been through this last generation, is something the country simply can't afford.

So put aside the search for goats, Mr. President. If something's wrong with the program, say so and fix it. The choices ahead could not be harder, nor the stakes for the future higher. This battle is going to be hard enough to win without fighting it on false fronts.