When Jimmy Carter was running for President last year, there was a good deal of confusion about where he really stood on key economic and social issues.

To many obeservers, the candidate seemed to be making promises that often appeared contradictory. Even after the election, voters were fretting nervously that they "didn't know" Carter very well.

Today, 10 months after the candidate took office, the uncertainty is continuing, but for a very different reason:

It's not that Carter hasn't taken firm stands on major economic problems. The problem is, whenever any of his proposals has been critized, he's shifted to the opposite position.

"In essence, the President has been formulating his policy by reaction," says one veteran analyst here. "It's no wonder so many people still are confused."

To many observers, the zig-zagging has been especially evident in the economic area, where policy shifts have spawned so much uncertainty that businesses are hesitating to invest in new plant and equipment.

The situation has become so bad that top Carter policymakers have begun to pull back from their earlier plans for more sweeping economic proposals and settle instead for more conventional measures.

The White House disclosed last week that the President is planning a major new push in January to "clarify" his economic policies and "make them more coherent" to the public. "We know we have to do it," one insider says.

The policymaking by reaction has been most conspicuous in Carter's tax-revision effort. The President promised in the campaign to overhaul the entire tax system. And as late as last fall, he was preparing to do just that.

When the more comprehensive package ran into opposition, however, Carter dropped his earlier promise and instead began shaping a new, sharply pared-back program centered primarily on standard tax reductions.

Most analysts now believe that "tax reform" essentially is dead.

The same pattern has appeared in the administration's position on money and credit policies. Only a few week ago, the White House was campaigning vocally for an end to the Federal Reserve Board's credit-tightening.

Top Carter aides left little real doubt that there was a serious policy dispute with the Fed's conservative chairman, Arthur F. Burns. In one apparent gaffe, the battle even made it to the White House bulletin board.

When the attack began drawing counterfire from the business community, however, the President ordered a stop to all public grousing about the Federal Reserve, and began heaping praise on Burns, who is a symbol of the board's tight policies.

At his last news conference, Carter denied any rift at all.

Carter also flip-flopped under pressure on the controversial Humphrey Hawkins "full employment" bill - liberal-sponsored job-creation measure that many economists have critized as unrealistic.

In the 1976 campaign, the Georgian opposed the meaure on the advice of his economists: the Carter camp seemed unanimous that the legislation would be a disaster.

But when a stray remark got him in trouble with blacks, Carter shifted to support the bill as a gesture to civil rights leaders. Earlier this month he endorsed it formally, and pledged to work for its passage.

There also have been other switches: The President recently began portraying his coming tax package as a vehicle to spur new investment. The shift followed corporate criticism of his Social Security and energy tax proposals, which hit companies particularly hard.

And earlier, the President dropped a long-promised anti-inflation promised because business and labor objected to preliminary plans for a system for early warnings on wage and price increases.

To be sure, some of these shifts appear merely to be a recognition of reality. As critics have pointed out, many of Carter's campaign promises were unrealistic.

When he assumed office, one analyst says, "he had to moderate some."

(Indeed, Carter began retrenching almost as soon as re was inaugurated. The 6 per cent economic growth target he set during the campaign was recalculated in March on a new basis that required only 5 per cent growth.

(And his promise to balance the budget has slipped - realistically - to a vow to eke out a small surplus only if the economy is at high employment - another way to concede that a continued deficit is likely.)

But to some observers, the effect has been to make the administration's economic policy seem contradictory - and almost bewildering.Tere are these examples:

On one hand, the President is maintaining his posture as a budgetary hard-liner, pushing to limit all spending boosts next year to simple cost-of-living increases - rejecting appeals for bigger outlays.

On the other, Carter has committed himself to a sizable new $7 billion to $10 billion urban financing program for fiscal 1979, and is still planning to push hard for welfare revision next year - a costly new program.

Carter is vigorously trying to court business in an effort top rebuild confidence and spur new investment - signaling nervous corporate chief-tains he won't do anytihing drastic that might exacerbate inflation.

At the same time, this month he endorsed the Humphrey-Hawkins bill, which to most businessmen is anathema. The measure would commit the government to reducing joblessness to 4 per cent by 1983 - a move most say would risk new inflation.

Carter promised during the campaign to overhaul the tax system and make it more progressive - a pledge that implies a sizeable redistribution of income from the rich to the poor.

But the latest version of the tax package Treasury drafters are planning would contain virtually none of the President's original proposals.

The administration has dropped a key provision to end breaks for capital gains.

Carter's promise to reduce appears to many analysts to conflict with his recent agreement to a sizable boost in the minimum wage - a move he opposed first, but then backed under pressure.

Economists say raising the minimum wage sharply makes employers less eager to hire so-called "marginal" workers, such as teenagers and low-skilled adults. It could also hurt employment in other areas as well.

And the President's efforts to slow inflation have been undercut repeatedly by the timing of his Social Security and energy tax increases and his support of such potentially inflationary measures as the cargo-preference bill.

As a result, there is still a good deal of confusion about where Carter really stands on key economic and social issues. And some analysts believe it will take more than a speech to clear the disparities away.