Tax-cut politics are rapidly pushing President Carter into a tactical shift that is almost certain to be interpreted as another in a long string of policy reversals.

Facing an election-year stampede by Senate Democrats following last week's surprise tax-cut proposal by Republical presidential candidate Ronald Reagan, Carter is being urged by some key advisers to make his own tax-reduction plans public soon, before Congress bolts out of control.

If the president does propose a 1981 tax cut soon, it technically will amount only to a speedup of his timetable. Carter had already indicated he would favor a 1981 tax cut, but wanted to delay congressional action until January for fear of reviving inflationary expectations.

Top presidential advisers, who concede privately the president almost certainly will have to act soon, are fretting that the shift will bring on renewed criticism that Carter is zigzagging, as he has several times before.

The Georgian's surprise turnabout in withdrawing his now famous $50 tax rebate proposal a few months after he took office earned him an early reputation for shifting policy in mid-stream. In his three and a half years as president, Carter has gone through four different anti-inflation programs. His next reversal on economic policy, if it comes, will be the second this year.

Carter began 1980 firmly opposed even to talk of any tax cut this year or next. His January budget called for allowing Americans' tax burdens to rise to postwar record levels, restraining spending moderately, and a modest $15.8 billion deficit.

Policymakers described the January spending plan as "austere." But the reaction across the nation was fear that the deficit would bring on a new wave of inflation -- an impression that was bolstered when consumer prices began soaring in January and February in part because of earlier oil price increases. Almost overnight, the financial markets went into panic. Interest rates skyrocketed.

Just four weeks after he unveiled the fiscal 1981 spending plan, the president was forced to execute his first flip-flop and began making plans to constrict the economy sharply. Spending had to be slashed and markets to be calmed.

The result was Carter's March 14 anti-inflation plan, which proposed sharp cuts in domestic spending to eliminate the budget deficit, plus an oil import fee and new credit controls on consumers and business. Under the administrtion's new policy, the number one goal was to balance the budget.Tax-cut legislation would have to wait until early next year.

This policy, too, was to be the victim of hapless timing. Unknown to Carter, the credit-tightening took hold just as the economy finally was falling into the long-predicted recession. The administration's new restraints merely hastened the drop and made it steeper.

Carter tried to remain on course, calling on Congress to balance the budget first before thinking about any tax cuts, despite the deteriorating economy. But the recession mushroomed quickly. Within a few weeks, the jobless rate was soaring and his plans for a balanced budget were shattered.

In part of calm recession jitters, the administration let it be known in early June that the president's advisers were considering a tax cut, agreeing to explore the question when Congress had shown adequate spending restraint -- a bow to the reality that budget-balancing was now impossible. But the president still wanted to put off legislation until 1981.

That timetble was upset, however, last week when candidate Reagan, seeking to pre-empt Carter on the tax cut, repackaged his own proposals into a call for a 10 percent across-the-board reduction in 1981.

The impact was immediate. Within 24 hours, edgy Democratic senators had abandoned Carter's hold-the-line stance and pledged a tax-cut bill of their own, to be considered no later than Sept. 3. House leaders conceded they inevitably would have to follow suit.

Late last week the administration began a move to regain control of the situation by agreeing to work jointly with House and Senate Democrats on a party-wide tax-cut strategy between now and the Aug. 11 start of the Democratic National Convention. The prospect that Carter will unveil his own plan soon has risen greatly.

Key presidential advisers still fear that enactment of tax-cut legislation this year could reignite inflationary fires in the financial markets, send consumers on another buying spree and undo the past few months' progress against inflation -- even if the actual cut doesn't occur until 1981.

But Carter is in a box. If he doesn't act soon, he could lose control to Congress. If he does, he might exacerbate inflation. It will probably look like zigzagging no matter which way he goes.