The collapse of Shahpour Bakhtiar's government in Iran yesterday after it was abandoned by the military thwarted both the expectations and the strategy of the White House and left the administration unable to state a policy for dealing with the rapid developments now overwhelming a once key U.S. ally.

With U.S. influence in Iran sinking to its lowest level in four decades, the administration refused all public comment and turned its immediate attention to the security of the U.S. embassy in Tehran and the estimated 7,000 American civilians, military advisers and diplomats still in Iran.

In an emergency meeting in the White House situation room, the Cabinet-level Special Coordination Committee chaired by national security affairs adviser Zbigniew Brzezinski reviewed contingency plans for safeguarding or evacuating Americans, officials said. They refused to disclose details.

The only publicly announced move was the shifting of six large passenger-carrying HH53 military helicopters and a detachment of 69 Marines to an undisclosed location near Iran. The Marines and helicopters were reportedly en route to Incirlik, Turkey.

The Pentagon and the State Department emphasized that the moves "are purely precautionary" and said there were no current plans to send the troops and helicopters into Iran. The Marines would be moved in only if the 19 Marines now guarding the embassy in Tehran need reinforcement, spokesmen said.

The moves were requested by U.S. Ambassador William H. Sullivan, whose recall from Tehran now becomes a strong possibility because of his close identification with U.S. support for Shah Mohammad Reza Pahlavi and the Bakhtiar government over the past year of crisis and upheaval in Iran.

Ironically, Sullivan's strong advocacy for the shah appeared to have given way in the past two months to more pessimistic but accurate reporting on the growing strength of the forces of the Ayatollah Ruhollah Khomeini and the need for the Carter administration to come to terms more quickly with that development. But, as it did with the shah, the White House felt compelled to stand publicly with Bakhtiar even though many of the administration's working-level experts and its intelligence reporting strongly suggested that Bakhtiar would not be able to hold the U.S. trained and equipped Iranian military behind him in a showdown.

After the shah's departure on Jan. 16, American policy focused on two points -- the unity of the armed forces as the nation's only bulwark against anarchy and civil war, and Bakhtiar's role as a constitutional stand-in for the shah.

The administration dispatched Gen. Robert Huyser, deputy commander of U.S. Forces in Europe, to Iran in late December to urge the military to remain united and loyal to the constitution (and thus to Bakhtiar), and not to attempt a coup.

Senior U.S. officials meanwhile portrayed Bakhtiar as the necessary symbol of continuity to reassure the military leadership which had been totally loyal to the shah. Bakhtiar's participation in or blessing for a new coalition government was needed to keep the military from falling apart, officials said.

Khomeini's dramatic return to Tehran on Feb. 1 rapidly transformed that equation and the U.S. role in efforts to bring about an orderly transition, however. Yesterday's events suggested that U.S. policy never caught up with the change Khomeini's return brought.

Almost immediately, the Iranian military leadership opened indirect negotiations with Khomeini, according to still sketchy reports. There were direct military contacts with Khomeini's choice as "revolutionary prime minister," Medhi Bazargan.

In both instances, the talks were held without Bakhtiar and without U.S. diplomatic representatives who had helped set up talks involving the forces of Khomeini, Bakhtiar, the army and the National Front political opposition. U.S. diplomats reportedly sat in on some of those talks.

This development significantly reduced already shrinking U.S. influence, administration sources feel, and opened the way for a separate deal that would exclude Bakhtiar.

Moreover, American ability to anticipate events was hurt by a drop in political reporting and field intelligence due to the reduction of the number of Americans in Iran from 45,000 to 7,000 in two months. Assessments became narrower as fewer and fewer officials in Washington were allowed access to the reporting out of fear of public disclosure of administration deliberations.

But testimony on Capitol Hill and authorized background briefings by senior officials left reporters with the impression that the State Department was strongly urging the White House to disengage partially from Bakhtiar's fate.

Intelligence reports reaching Washington stated that army units were switching allegiance from Bakhtiar to neutrality or to supporting Khomeini openly. Other reports originating in the State Department last Monday portrayed Bakhtiar's government as being in its final days.

Those reports are known to have angered President Carter. He immediately let it be known through aides that he had been told on Monday by Gen. Huyser that Bakhtiar's chances were improving daily and that the military had become more cohesive in the wake of Khomeini's return.

A shift came Saturday, however, when Andrew Young, U.S. ambassador to the United Nations, announced that he had met with two of Khomeini's representatives in New York with State Department approval. The State Department previously had refused to disclose the nature of contacts with Khomeini representatives and had said the United States would not talk to Khomeini directly.

After participating in the taking of the Iranian embassy yesterday, one of the representatives Young saw, Shahriar Rouhani, told reporters that there were "genuine grounds" for a good relationship between Khomeini's Islamic Republic and the United States. He added that the administration should make "a gesture" toward the ayatollah.

Rouhani stressed his concern over U.S. contingency plans, and called on the administration to renounce publicly any military action in Iran. He also said Washington should immediately recognize Khomeini and establish a dialogue with the Moslem leader.

Yesterday's burst of activity at the White House and the State Department, where an Iran working group assembled, was carried out without any public recognition of the changes taking place in Iran.

U.S. officials said there was a strict order not to comment on the changes. White House spokesmen referred reporters to State Department duty spokesman Ken Brown, who said he could not comment on U.S. policy toward Iran.

Brezezinski telephoned President Carter, who spent the weekend at Camp David, three times during the morning to brief him on events, and convened the meeting of the Special Coordination Committee, the administration's highest-level crisis management body.

Secretary of State Cyrus R. Vance, who was reportedly in New York Saturday, was not present at the meeting. Vance met Carter later in the day at Camp David, U.S. officials said.