The preoccupation of Congress and the White House over the last few months with reducing the budget deficit has obscured this basic fact:

On the issue of taxes Ronald Reagan may be in the midst of a fundamental reversal of economic policy.

The centerpiece of the president's original economic program last year was the enormous tax cut he proposed for individuals and business. The $749 billion reduction over six years represented a major achievement for an administration that in many ways views the federal tax system as a detriment to economic development.

Some critics said the tax cut, especially when coupled with the defense buildup the president was also insisting on, would create unmanageable deficits. The supply-siders advising the president discounted this. They argued that tax cuts were the tonic the economy needed, that they would bring on added growth, that this growth would in turn generate new tax revenues. In this painless formula, the tax cuts would thus pretty quickly pay for themselves.

So far, however, that hasn't happened, and now, to reduce the forthcoming deficit and help bring down the high interest rates that are choking off growth, leading members of Congress in both parties, many of the president's aides and to some extent the president himself are considering raising taxes.

Though it was glossed over at the time, the president has already reversed himself significantly on last year's business tax cut. He proposed in his February budget a new minimum tax on corporations that, along with certain other provisions, would raise an additional $9.1 billion from business in fiscal 1983.

In doing so, these proposals would take back about 65 percent of the $13.9 billion cut in business taxes for 1983 that Reagan pushed through Congress last summer.

Now White House and congressional budget negotiators are discussing other sizable tax increases, including a "surtax" on upper-income individuals that would take back part of the 10 percent cut in individual income tax rates scheduled for this year.

The president and his aides, who came into office committed to avoiding the flip-flops that characterized the Carter presidency, have gone to great lengths to say that these new proposals do not constitute a reversal.

They began by playing games with vocabulary; they were not proposing tax increases, they said early on, just modest amounts of "revenue enhancement." Now they are making further distinctions. This year's increases would not be a reversal of last year's cuts because the provisions of the tax code that would go up this year are not the same as the ones that went down a year ago.

Thus the president at a news conference last Tuesday reaffirmed his support for the "tax program of ours which is based on providing an incentive, both for individuals and business--the business tax cuts, the across-the-board three-year cuts in personal income tax. Now I have not changed on that."

And a few days ago Murray L. Weidenbaum, chairman of the Council of Economic Advisers, said this to reporters when asked whether a surtax would be a partial cancellation of the individual tax cut:

"In terms of the concept, it doesn't violate the president's program . . . . It dilutes some of its effect . . . . The notion of a temporary surcharge to deal with a temporary budget problem to keep in place a permanent tax cut does not do violence."

The president at one earlier point declared he was firmly opposed to any "tampering" with the three-year tax cut for individuals because it would "inflict major damage on the economy."

From the vantage point of a well-to-do taxpayer, it is hard to see how a 4 percent surtax does not represent tampering with a 10 percent tax cut.

The same is true for a businessman who took the administration at its word last year, thinking that if his company invested in new equipment, it would be eligible for tax breaks that in effect would wipe out all taxes on the profits from those investments. Now he is looking ahead to a possible 15 percent so-called minimum tax that would alter that expectation.

The administration, however, is not alone in violating some of its claimed goals.

A number of key Democrats, including House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), are calling for repeal of the scheduled third installment next year of the individual tax cut on the grounds that it would help restore equity and fairness to the tax system.

Tax equity is impossible to define. From one point of view, elimination of an across-the-board 10 percent tax cut might be considered to hurt those in the lower brackets less than those with high incomes because the rich pay a higher proportion of their income in taxes.

But from another vantage point, the Democrats' position would appear to be significantly unfair to the working and middle class constituents they want to protect. Because the 1981 tax bill immediately reduced the top rate on unearned income from 70 to 50 percent, and the capital gains tax rate from 28 to 20 percent, the very rich have already gotten most of the benefits they can expect from the legislation.

For those earning $200,000 or more annually, repeal of the 10 percent rate cut scheduled to go into effect July 1, 1983, would mean the loss of only 5 percent of all their likely tax breaks under the legislation. For everyone else, however, repeal of the third year would represent a loss of 32 to 40 percent of the breaks.

The scope of some of the tax increases under consideration by the administration and Congress is reflected by the following: on the corporate side, the administration's "minimium" tax would apply to about 90,000 businesses; on the individual side, one suggestion is to set a 4 percent surtax on incomes in excess of $40,000, a step that would increase taxes for these people by about $4 billion annually.

The administration has justified some of the new proposals on the grounds that they close unjustified tax loopholes, but the minimum tax clearly functions to weaken the benefits of the investment tax credit and a number of other tax preferences supported by the administration, including tax leasing.

Along with the new depreciation schedule, the investment tax credit is the core of the business tax cut in the president's 1981 tax bill.

In a comment on the policy reversal implicit in the administration's advocacy of a minimum tax on corporations, Emil Sunley, former Treasury tax specialist and now tax analyst for the accounting firm of Deloitte Haskins and Sells, said, "It won't pass the 'red-face test.' "

What does that mean? That in light of the past administration rhetoric there is no way to justify the new tax proposals before Congress without embarrassment.