Pointing to recent and largely temporary gains in the nation's leading economic indicators, the supporters of the supply-side economics, which underlie the Reagan administration economic policies, have begun to proclaim the accuracy of their prophecies. These proclamations are at best misguided and at worst, dangerous. In fact, public perceptions of an improved economy rest largely on myths, including these:

Federal spending has been reduced. Wrong. Under President Reagan, federal spending has increased 30 percent, from $657 billion to $854 billion annually, and now consumes 24 percent of the nation's GNP -- a peacetime record.

There has been considerably more economic growth under the Reagan administration. Wrong again. In the past four years, real GNP has grown at an average annual rate of 3.01 percent, hardly more than the corresponding 2.95 percent figure for the Carter years.

The tax burden has been reduced. Not really. After adjusting for inflation and increased payroll taxes, the real after-tax income for middle-income families ($15,000-$50,000) has remained essentially the same as it was four years ago. And while the tax burden has been vastly reduced for the wealthy and large corporations, it has actually increased for families making less than $10,000.

Reducing taxation of wealthy individuals and corporations was necessary to increase business investment and productivity as well as personal savings. If that was the strategy of Reagan's 1981 tax reform, it simply hasn't worked. Under the Reagan administration, real business investment has remained relatively constant. Under the Carter administration, by contrast, investment increased approximately 18 percent. Industrial productivity has increased less than two-tenths of 1 percent since 1981, and in the critical industries such as steel and iron, productivity has dropped a whopping 23 percent. Personal savings have also plummeted to historical lows.

The unemployment picture has improved under Reagan. Still wrong. Unemployment, which has started rising again, is at 7.5 percent, the same as when Reagan took office in 1981. Five million fewer jobs have been created under Reagan than under Carter, and 500,000 more people are out of work today than when Reagan took office.

Inflation has certainly been licked. Only momentarily. Tight monetary policy (reducing monetary growth from 7.8 percent to 6.2 percent annually) reduced inflation from 9.4 percent to 4.1 percent annually but mired the country in the worst unemployment and most severe recession since the Great Depression. To pull the economy out of this mess in time for the election, the tight monetary policy was reversed and monetary growth was increased in 1983 to 9.5 percent -- higher than any other time at least since World War II.

The advantage of such a strategy is that increasing monetary growth will always create temporary economic gains and give voters the impression that the economy is improving. Historically and inevitably, however, the gains are elusive and soon disappear, being replaced by higher prices. According to economist Milton Friedman, "we shall be fortunate indeed if prices are not rising in the 7 to 10 percent range by the fourth quarter of this year and in double digits by 1985."

At that time, however, there will be an added dimension to the economic picture: a staggering $200 billion federal deficit guaranteeing an overvalued dollar and chronically high interest rates. The 33 percent overvalued dollar has already produced a projected record-breaking $110 billio annual trade deficit that translates into some 3 million lost jobs -- jobs that may never be recovered.

The deficit has also kept interest rates at persistently unaffordable levels for most Americans and has precipitated an almost 300 percent increase in business failures as well as unprecedented increases in mortgage delinquencies. Housing starts and industrial capacity are substantially lower today than they were in 1981, and both promise to worsen because of the deficit.

The federal deficit, coupled with loose monetary policies, necessarily means that there must be a day of reckoning. Just ask the nation's leading economists and Wall Street speculators, 70 to 80 percent of whom, according to recent polls, expect a recession soon, questioning only whether it will come now or after the election. This is the real Reagan economic record and what it promises for the future.