Until this week, one might have labeled President Reagan's push for the Kemp-Roth tax cut in 1981 his most irresponsible fiscal action.

After all, it contributed to a doubling of the national debt from $900 billion to $1.8 trillion, a national crisis over our huge trade deficit, and transformation of the United States from a creditor to a debtor nation.

But Reagan's decision to torpedo his Senate Republican leadership's efforts to trim the $200 billion annual deficit may outrank the irresponsibility of 1981.

The last-minute compromise adopted by Congress late Thursday -- labeled by Sen. Robert J. Dole (R-Kan.) as "better than nothing" -- claims to make substantial reductions. But these claims rest on dubious economic and legislative assumptions. And even so, the hastily pasted together package, by its authors' own calculations, would result in a deficit of $172 billion next year and leave untouched the major questions of indexed Social Security, other entitlement programs, and the need for a tax increase.

According to an estimate by Henry Kaufman of Salomon Bros., the situation is even worse: Kaufman projects the fiscal 1986 deficit at $190 to $200 billion, meaning a savings at best of $20 billion from fiscal 1985.

Among other things, the cosmetic compromise thrown together assumes a six-year stretch -- from 1982 to 1988 -- of no recession, with interest rates continuing to go down, and a nice, smooth economic growth pattern averaging at least 4 percent. This defies logic and past experience.

Thus, the president's decision to turn away from the most urgent design of a budget package, as recommended to him by Dole and Sen. Pete Domenici (R-N.M.), still means:

*Continuing high deficits that are likely to push interest rates higher, accelerating the onset of a new recession.

*A policy dilemma whenever a new recession begins: It will be more difficult to rejuvenate the economy with standard fiscal policy measures, putting the entire burden on a loose monetary policy.

*A probability that another nail has been driven in the coffin of tax-reform legislation for this year. But even if tax reform survives, the likelihood grows that it will fail the "tax-neutrality" standard. Instead, it would add to the deficit.

*New momentum for protectionist legislation as it becomes clear that the trade imbalance will get no help from a change in U.S. macroeconomic policy.

*A further decline of foreign confidence in the U.S. economy. The sharp drop in the bond market over the last couple of weeks is attributed to the conviction among traders that Congress and the administration will do nothing significant on the budget.

The huge deficit, which now promises to go on for the foreseeable future near the $200 billion level or higher, is the single most worrisome economic fact of our times. It is primarily the U.S. deficit that keeps real interest rates and the dollar too high, sucking imports into the country at a rate triggering a trade deficit of about $140 billion to $150 billion a year.

Ironically, the president's decision that he couldn't support a $5 fee on imported oil (that's a tax increase, therefore against his principles); or any constraints on Social Security cost-of-living increases; or any changes in indexation of tax brackets, came on the same day that Japan announced details of its "action program" designed to promote imports.

The general reaction to the Japanese proposals among congressmen and businessmen was one of skepticism (including negative comments from some senators who admitted they hadn't bothered to read the documents). But if this country is skeptical of the Japanese commitment to tackle the trade imbalance, what should the Japanese reaction be to Reagan's outright refusal to take action to cut the budget deficit?

The danger now is that the protectionist bloc will gain additional strength: It can no longer be hoped that a gentle decline in the dollar exchange rate this year (it's down about 13 percent since March) will continue, helping to ameliorate the trade deficit.

It is also possible that the American inability to control the budget could lead to a collapse of the dollar. The Federal Reserve Board is feeding reserves into the economy to foster a second-half recovery. With no help in view from fiscal policy, at some point the Fed will have to reverse its course and tighten up substantially. Foreign-exchange markets, Kaufman points out, could read that as a sign of national weakness, as they did in 1979, when interest rates were high and the dollar plunged.

If the Fed takes the other course, keeping money easy to sustain the recovery during the 1986 election, it could mean the onset of a big new inflation, says Jack Albertine, president of the American Business Conference. Albertine suggests that by early 1986, departures of two members of the Fed Board of Governors will produce a "supply-side majority" bent on creating fast growth without regard to the deficit.

Albertine says his group, a pro-business lobby, will urge the president to call a national conference this summer among business, labor, and consumer groups to forge a political consensus for a more meaningful budget-reduction package. "The problem is not analytical, but how to mount a mechanism to generate the necessary political will," according to Albertine. He thinks the need for such a conference is underscored by the continued failure of Congress to bring the deficit under control.

Anything, I suppose, is worth trying, inasmuch as the President of the United States -- painted by the publicists who sold him to the American people as a fiscal conservative -- is content to preside over the biggest budget deficits in our history, rather than support even the mildest form of tax increase.

Almost everyone in Washington, including most of his most stolid supporters on Capitol Hill, thinks the president is on a collision course with disaster. Some of the things Senate Republicans are saying can't be printed in a family newspaper. But no one seems able to do anything significant about it.