There is a tendency in some quarters to scoff at the importance of the perplexing federal budget deficit. Does the deficit really matter? skeptics ask. After all, the sky hasn't fallen, despite the huge deficits piled up by President Reagan. Thus, Tom Wicker, a political columnist for The New York Times, suggests that all the talk about deficits represents "hysteria along the Potomac."

Wicker says the economy has been doing well, and -- in fact, the deficit has been "a major stimulus to solid economic growth." So why worry? Some others who debunk the deficit problem point out that predictions that investment would be "crowded out" by high interest rates have not been borne out. (Instead, American investment and exports have been crowded out of foreign markets.)

Then, economist Isabel Sawhill of the Urban Institute comes along with a piece in The Times to remind us that, although the long-term damage of the deficits is both "real and serious," disaster is not imminent, "contrary to public opinion."

Most of the deficit-worriers I know haven't been predicting a financial crisis as of next Sunday at 11 a.m. Rather, like Sawhill, they have stressed the long-term (and cumulative) ill effects from the deficits. But her point is worth making: The very fact that the dangers are intangible at the moment is part of the problem in getting the full meaning of the situation across to the public.

The average citizen is not going to worry about the deficit so long as he or she has a job and inflation is under control.

That's why Reagan economic adviser William A. Niskanen Jr. calls the deficit "a slow-acting but potentially lethal cancer." John H. Makin of the American Enterprise Institute adds that, because disaster has been averted in the past few years, some have been "emboldened . . . to claim that no action (on the deficit) is needed now. Such reasoning is dangerous. We may well be lucky for another year, but the passage of each month . . . worsens the odds. Why keep testing our luck until it fails to hold?"

Even top officials of the Reagan administration who downplayed the deficit problem all through the 1984 campaign finally have conceded that sustained economic growth won't be enough by itself to cut deficits back to safe levels.

This is the hard reality: The overall debt is growing at a faster rate than the economy itself. Reagan's own budget document shows that the gross federal debt at the end of calendar 1980 was $914 billion and will rise by the end this year to $1.841 trillion. It could triple to $2.5 trillion by the end of the decade.

How big can the debt grow? Already, the national debt held by the public has risen from 28 to 37 percent of the gross national product just since 1980. And the Congressional Budget Office now estimates that if policies aren't changed, the federal-debt-to-GNP ratio will rise to 50 percent by 1990.

The importance of this number is that it suggests that not much will be left over for the private economy after the Treasury does its borrowing. A CBO study based on work by Makin and Raymond D. Sauer suggests that every one-point increase in the public-debt-to-GNP ratio cuts private investment by about $75 billion.

"Historical evidence provides little guidance for gauging the precise economic effects of peacetime deficits of such magnitude and duration, but they clearly imply adverse consequences for long-run standards of living," the CBO said. Translating the bureaucratese: We don't know just how bad a recession we'll wind up with because we never had a comparable situation before -- but it will be plenty bad.

The crucial fact is that the national debt is feeding on itself: Every time there is an additional $200 billion annual deficit, there is also another $20 billion to be tacked on for the interest on that new piece of debt.

Interest on the debt, according to the CBO, is the fastest growing component of the budget -- swelling faster than entitlement programs or military spending.

Ten years ago, interest payments on the debt amounted to a mere $23 billion, or 7 percent of the budget. In 1985, interest costs soared to $130 billion, or 13.7 percent of the total budget. By 1990, according to the CBO projection, interest payments will run to $230 billion, or 16.6 percent of the budget.

Budget Director David A. Stockman pulls no punches: "The president realizes that this is the last opportunity to restrain government and to reduce its size," he told a press conference.

And listen again to Niskanen: "There is no way to avoid either present or future taxation for the current level of government services. It must be financed by taxes sooner or later . . . Borrowing only puts off the time in which the taxes have to be raised."

A basic mistake columnist Wicker makes is to assume that the economy is strong and healthy despite the deficits.

In his first major speech since taking over the helm of the New York Federal Reserve Bank, E. Gerald Corrigan -- who some see as a possible successor to Fed Chairman Paul A. Volcker -- made the point that the current economic recovery from a very severe recession has left many important weak areas. He said:

* Unemployment is still too high, especially for the third year of an expansion.

* Many sectors of the economy (agriculture, notably) that have not shared in the general advance are vulnerable to any fall-off in economic activity.

* Protectionist pressures are serious and growing.

* Many domestic bank loans don't meet "quality" standards (agriculture and oil, for example).

* The debt burden of the Third World may have been alleviated, but it has not been solved.

Most importantly, Corrigan warned, "A falloff in economic activity would aggravate the budget deficit and erode the political will to reduce its "structural" component.

A major part of the problem, as Stockman admitted last week, is that the Reagan administration, with the help of Congress, seriously eroded the tax base.

"The original 1981 tax cut clearly went too far," Stockman told the House Appropriations Committee. Tax-boosting bills in 1982, 1983 and 1984 only partially recovered the loss.

Niskanen and Stockman, like the president, would prefer to get the deficit down by cutting spending rather than by raising taxes. But that's a bullet politicians won't be able to duck much longer. "The arithmetic answer is that we cannot increase federal debt relative to the size of the economy indefinitely. That ratio has got to stabilize, and the president's budget stabilizes that ratio by 1988" at 40 percent, Niskanen said.

"But if that ratio keeps going up, going up, you either are going to have a progressive reduction of noninterest spending, or a progressive increase in tax rates. Now, that is an either/or. It doesn't say it has to be spending or it has to be taxes."

So the answer to the notion that there is "hysteria" on the Potomac is very simple: Some sensible people are saying that, if we continue to go the way we are going, the government eventually will have to abandon a large part of its normal operations -- defense and nondefense -- just to be able to pay interest on the old debt. Or it will have to raise taxes to pay all its bills, and raise them a lot.

This would create a drastic crowding out of the private economy, higher interest rates -- in effect, the lower standard of living mentioned by the CBO. The only reason this hasn't yet happened already is that the United States has been importing vast amounts of capital from abroad -- to finance the deficit -- at levels that common sense suggests can't be sustained indefinitely.

Is there no other choice? Yes, the CBO reminds us: The Fed can pay off the debt by cranking up the printing presses, leading to hyperinflation. Remember the history of Germany after World War I? Do you want to push a wheelbarrow loaded with greenbacks to the grocery store for a bottle of milk and a loaf of bread? You may have to, unless Democrats and Republicans alike decide that the deficit is no laughing matter.