After three years of battering at home and abroad, the Carter administration's foreign policy is reeling from a series of body blows in the past two weeks.

A fortnight of failures -- to some extent self-inflicted, to some extent imposed by forces beyond the administration's control -- has shaken confidence in American policymaking at a time when U.S. interests and the lives of Americans are a dramatic risk overseas.

Judging from headlined reversals, March, rather than the poet's April, would seem to be the cruelest month:

March 1 -- The United States votes in the United Nations Security Council for a controversial resolution criticizing Israel.

March 3 -- The White House disavows the vote as a mistake.

March 7 -- Statements in Washington and Islamabad confirm the failure of the high-priority U.S. program of military aid to Pakistan.

March 10 -- The United Nations commission's plans to bring about release of American hostages collapse in Tehran.

Throughout the period, there was a rising chorus of concern about the unity and momentum necessary for an effective U.S.-Alied response to the Soviet invasion of Afghanistan.

Whatever the precise mix of mistakes and misfortunes -- a question much debated among foreign affairs specialists -- the March events have generated renewed examination of policy and policymaking in the Carter era. Insiders and outsiders alike are examining the underlying causes of the recent reverses. Among their conclusions:

At the end of three years, President Carter and his senior advisers have no clear and common strategy for dealing with a troubled world.

"Carter has no political philosophy" and therefore no central concept or organizing principle in foreign affairs, said one of his senior planners. Said another high-ranking official: "If you open the hood, the policymaking motor is finely tuned and running well -- but if you open the glove compartment, there is no road map."

During most of the first three years, the Carter administration was beset by fissures along the fault line of its policy toward the Soviet Union, the most crucial aspect of American diplomacy and military power in the nuclear age. But starting last Nov. 4 with the seizure of American hostages in Iran and particularly after the Soviet invasion of Afghanistan last Dec. 27, the familiar Cyrus R. Vance-Zbigniew Brzezinski gap was closed in a tightly focused concentration on reaction to momentous events.

After four months, the unity and shared resolve that stemmed from crisis is beginning to erode. There is a sense among some insiders that a phase is coming to a close. If so, it leaves a set of commonly agreed reactions open to immediate challenge, but leaves no long-range plan for dealing with Soviet power.

In the absence of stable policies, Washington is prone to overnight shifts and lurches that are difficult for others to follow.

The Soviet adversary as well as European allies complain that U.S. policy has become unpredictable, inconsistent and a poor basis for planning. This is all the more vexing in the case of the allied because of Carter's tendency toward policymaking by pronouncement -- to proclaim first and consult later.

Carter announced his Persian Gulf doctrine for the muscular protection of the oil-rich region without consulting or even informing the nations in the Persian Gulf or Japan and the nations in Europe, which are heavily dependent on Persian Gulf oil. (He also did not consult Congress in any real sense of the word.)

After weeks of pressuring its allies to place tough economic sanctions on Iran, Washington announced the shelving of its sanctions policy without informing its allies.

Carter announced an aid plan for pakistan before he worked it out with Pakistan. Trouble followed.

In view of Carter's tough race for reelection, domestic political requirements have begun to weigh more heavily on foreign policy.

Campaign manager Robert Strauss played a key role in disavowing the U.N. vote, which has infuriated Jewish voters. Carter's need for a show of immediate response to the Soviet invasion was a factor behind the premature announcement of the Pakistani aid plan.

The sudden anti-Soviet swing in U.S. policy is good politics at home. Along with the rally-round-the-flag sentiments arising from the hostage crisis, it has dramatically improved Carter's political prospects.

The management of decision-making and execution of decisions, recurrent weak points in Carter diplomacy, have become centralized and more consistent -- but now are afflicted by too many diverse decisions at once. m

Since Nov. 4, operational details as well as high policy have been decided in daily White House meetings of Carter's foreign policy advisers and a few aides. While this has expedited action, it has led recently to some hasty judgments and mistakes by overburdened and weary people.

"This is a severe case of system overload," said a well-placed congressional observer. "I see a group of tired, harassed, frustrated, near-cynical people up here day after day, trying to handle too many things happening to fast."

The Carter team is dealing with a world of the 1980s that is more dangerous and unstable than before, and is doing it with American resources that are not as large or as flexible as in the past.

Many of the most serious problems of the day are economic, flowing from oil prices that have risen to a level many nations are unable to afford. Worldwide inflation has weakened governments and political leadership and had diminished the economic and military resources to deal with multiplying problems.

"Soviet military power, internal instabilities magnified by mass communications, intractable regional conflicts and energy-economic disorders are going to whip through the 1980s like the Four Horsemen of the Apocalypse," said a senior U.S. policymaker. He is uncertain that this administration -- or any other -- will be equal to the task.