It's good to have President Reagan back, obviously fast on the way to a full recovery after a narrow escape from an assassin on March 30. A real-life John Wayne character, the president is riding a wave of extraordinary popularity, and his aides are counting on his enhanced clout to regenerate momentum for his economic proposals, especially for the three-year Kemp-Roth tax bill.

But the flush of good will we all feel toward President Reagan -- together with admiration for his grace under pressure -- should not dampen valid criticism of his economic recovery program.

The president insisted in his brief address to Congress Tuesday night that the "dream" of making this country strong again will come true if the nation buys his whole program, unaltered, on "faith."

The president is obviously a master on television. No one has ever been any better at it. President Carter bombed out during last year's debate with Reagan when he quoted daughter Amy. But Reagan neatly carried off, with his actor's sense of perfect timing, the introduction of a letter from second-grader Peter Sweeney in which Peter worried that Reagan might have to make a speech in his pajamas.

Rep. Robert H. Michel of Illinois, House minority leader, says the hold Reagan seems to have on the public makes doubters of the economic program feel, "Gosh, how can I buck that?"

Democratic congressmen point to polls like the one done by ABC and The Washington Post, which says in effect that voters may be dubious about the Reagan program, yet are solidly behind him.

For sure, that makes it tough to buck the president. But those Democrats who are convinced that the Reagan program is inflationary and tilted toward the rich have no choice but to challenge the president if they want to keep their self-respect -- to say nothing of preserving a nucleus of a political opposition.

There is an excellent economic case to be made against the Reagan program, which at one and the same time calls for a massive tax cut and a massive increase in defense spending that heavily outweigh the proposed cuts in civilian spending. The result is bound to be inflationary, and the only method proposed by Reagan to hold inflation in check is a brutally restrictive monetary policy that will drive interest rates up.

This case was outlined a few days ago in a speech to the National Press Club by New York financial expert Henry Kaufman, whose track record for accurate forecasting -- at a time when other economists have missed the mark by a mile -- forces serious attention to his views.

Increasingly, the evidence points to a surprisingly strong economy that doesn't need, and shouldn't get, the extra stimulus of the Kemp-Roth bill's $150 billion in tax cuts over the next three years. The economy needs some specific kinds of tax relief, better targeted, for business and for low-income groups severely affected by higher Social Security taxes.

Barron's editor Robert Bleiberg, noting the sharp 6.5 percent gain in real economic activity in the first quarter, broke ranks with many economists (including Reagan's), predicting that "by the end of the year, production and trade will be hitting all-time highs."

Kaufman made much the same point is his Press Club speech. "Many of my economist friends, who were, I thought, conservative, tell me that the economy is brittle," Kaufman said. "This was once the buzz word of my friends with liberal identities. They are now fearful of too large a fiscal stimulus. On the other hand, my conservative friends, who always advocated a balanced budget, now say a budget deficit to finance tax cuts is part of the essential transition for rebalancing the role of our government."

Kaufman does a simple exercise in arithmetic: In ficsal 1982, Reagan's tax cuts would amount to $54 billion, while the defense budget will increase $27 billion. That's a fiscal thrust of $81 billion. Against that, nondefense spending would be cut by $46 billion. Thus, there would be a net fiscal stimulus of $35 billion. More than that, Kaufman pointed out, the big bulge in defense spending (and commitments for even bigger outlays later on) pack an extra inflationary wallop.

Nonetheless, the Democrats seem ready to march in step with most of Reagan's nondefense cuts and with his defense budget increases. The chief effort to be made by "liberal" Democrats is a proposed modification of the Kemp-Roth tax bill, to squeeze some (but not all) of the benefits proposed for the rich into the middle and lower income brackets.

The net of all this is that the Democrats have thrown in the towel. Reagan is an authentic American hero, and the Democrats don't have the stomach for fighting him. "Support the president, that's the concern out there," said Massachusetts Democrat and House Speaker Tip O'Neill, "and Congress can read that. I've been in politics a long time, and I know when to fight and when not to fight.