Two months after he unveiled his "comprehensive" economic game plan, Jimmy Carter is back facing another round of important economic decisions - this time to patch up what has gone awry since January's blitz.

Prodded by anxious advisers, the president is considering a series of measures aimed at putting out new fires involving inflation, oil imports and Social Security taxes.

While only a few of these proposals constitute major changes individually, together they could amount to a significant revision of the economic plan Carter proposed in January.

Moreover, officials are cautioning that no matter what the president does, it may make only a marginal difference in the short run. Many of these problems will take years to resolve.

The changes come only eight weeks after Carter announced a spate of new proposals that were supposed to set the economy's course for the next year to 18 months - a new budget plan, a major tax package and an anti-inflation program aimed at persuading business and labor to moderate wage and price demands.

The outlook seemed relatively bullish then: The recovery was continuing at a strong enough pace, inflation seemed unlikely to worsen much, and the dollar appeared headed for a turn-around. Carter turned to other things.

Now, with the ink on those forecasts barely dry, the president is facing a series of new developments that abruptly have pushed the economy back onto the front burner and are forcing him to reconsider some moves.

William G. Miller, the new chairman of the Federal Reserve Board, argues that some of the programs Carter proposed in January no longer are viable. Among the "new" problems - inflation, energy and the dollar.

There are these developments:

Primed by unexpectedly volatile farm prices and more stubborn-than-anticipated wage patterns, inflation has erupted anew in the past two months, threatening to slow the economic recovery.

While economists appeared confident in January that inflation would run no higher than 6 to 6.5 percent this year, the administration's internal estimates now show it's likely to reach 7 t0 7.25 percent by yearend.

Moreover, the new anti-inflation program the White House unveiled with so much fanfare two months ago never has gotten off the ground. At the urging of his advisers, Carter now is considering toughening it somewhat.

Despite some visible moves by the Federal Reserve Board, the dollar has continued to fall on the foreign exchange markets, plunging to record lows almost daily against the West German mark and Japanese yen.

Some analysts now fear that unless the dollar rebounds by late summer, the government may be forced to take harsher steps, possibly even slowing the domestic recovery to bring it into line with Europe's growth rate.

Carter faces new pressure daiy for tough action on the currency question. Among the most ominous: King Khalid of Saudi Arabia has warned that unless the dollar inproves the oil countries may raise petroleum prices.

The energy bill the administration expected to see passed at the start of this year's congressional session still is stalled in conference, and shows few signs of emerging in a form that will have much immediate impact.

As such, Treasury Secretary W. Michael Blumenthal already is urging Carter to impose oil import quotas on his own if the energy bil hasn't passed by May 1. Several other aides are recommending tough action.

Although the economy still is expected to snap back smartly from the effects of the recent cold weather and the coal strike, their impact has clouded the outlook somewhat. Some are predicting a sluggish second half.

At the same time, the president is running into trouble with Congress on the economic and tax proposals he recommended in January.

His fragile tax package has been hit by a new challenge from law makers seeking to roll back the new Social Security tax increases. Any such move would require revamping Carter's income tax cut and "tax reform" plan.

(The original January tax package was headed for an overhaul anyway. House members have indicated they want to reshape the proposal to provide larger tax cuts for middle-income taxpayers and to scrap most of the "reforms.")

Finally, Carter's budget restraint goals are being threatened by costly new measures from an election-conscious Congress - including a multibillion farm bill and an expensive tuition tax credit proposal.

In January, the president recommended a budget deficit for fiscal 1979 of $60.6 billion. Now, congressional leaders are talking about a $70 billion red-ink figure, which could heighten infltion fears.

The series of new developments is partly Carter's fault and party just happenstance. Few could blame the administration, for example, for failing to foresee the continued decline of the dollar, which many view as irrational.

And the administration was hit with a lot of plain bad luck.For example, a part of the new inflation threat stems from a failure in the Brazilian soybean crop - a disaster that's raised grain prices here and later could affect meat prices.

There also have been other problems: The energy bill fell far behind schedule in Congress. The coal strike has lasted much longer than anyone expected. And even Miller's confirmation as Fed chairman ran into a snag in the Banking Committee.

At the same time, however, analysts say the administration has made several mistakes - among them seriously misjudging the economy's problems when it put together its January package.

Economists say some of those warning signs, such as the onset of new inflation, were visible then, but the White House simply may have been too starry-eyed to see it. Now, the problems are coming home to roost.

Critics also contend that the administration has failed to act decisively in several key areas, contributing to the problems it faces today.

For example, despite Carter's much-ballyhooed announcements in January, the administration never followed through on its anti-inflation program. The apparatus still isn't in place, two months after the unveiling.

And Carter forces have done almost nothing to ward off expensive new budget-busters, like the farm bill and the House Ways and Means Committee's plans to enlarge the tax package.

To top everything off, the president himself has been preoccupied with other problems, from the coal strike and Mideast question to the Senate vote on the Panama Canal treaty.

Unfortunately for the administration, all these issues seem to have come together at once. They have touched off a major policy debate among top economic officials, with Blumenthal and chief presidential economist Charles L. Schultze favoring a tougher stand on inflation and related problems.

The administration already has decided to continue its hard-line stance against congressional pressures to roll back this year's Social Security tax hikes. There's serious question, however, whether it can prevail.

This weekend, Carter is expected to consider proposals that he also take a tougher posture on the anti-inflation issue, both by stiffening his program and reaffirming that he won't allow the deficit to rise.

A decision on Blumenthal's oil import quota proposal also is said to be close, and the administration is keeping a close watch on the dollar.

Carter leaves Tuesday for a trip to South America, and so some of these decisions, if not all of them, may be postponed. But as critics keep pointing out, time is running short.