The Iran crisis ended its eleventh week yesterday, with the Carter administration's game plan for freeing the American hostages undergoing quiet but drastic revision because of the Soviet invasion of neighboring Afghanistan.

Until recently, the U.S. approach to Iran was one of pressure and rhetorical bellicosity, punctuated by veiled warnings that American impatience about the hostages could lead to military action, such as a naval blockade.

During the last few days, though, this stance gradually has been softened in a number of unadvertised but clearly perceptible ways. In place of the threats and name-calling, official U.S. pronouncements about Iran have taken on a conciliatory tone stressing the argument that Iran's real interest lies not in quarrels with the United States but in protecting itself against the Soviet threat.

Prompting the shift has been a major change in what administration strategists see as the fundamental problem confronting the United States in the unstable Southwest Asia region.

In their view, what began as a test of will between the United States and Iran's revolutionary zealots has been transformed by the Afghanistan situation into a U.S.-Soviet competition for access and influence in the Persian Gulf, with its vital oil supplies.

And, while no one will say so publicly, the administration considers the need to contain the spread of Soviet hegemony in the region more important to long-range U.S. interests than the release of the hostages or a demonstration that Iran cannot thumb its nose with impunity at the United States.

That, U.S. officials stress, does not mean President Carter is prepared to write off the American hostages or even soft-pedal concern for their safety. One senior official said candidly: "Even if we wanted to do something like that, public opinion would never allow us to get away with it. It would be sheer political suicide for the president."

But the same official conceded, "The new factors introduced into the situation by Afghanistan have forced us to review the bidding." The changes that have resulted from this review are easily identified by comparing the tack followed by the anministration toward Iran before and since the Soviet takeover of Afghanistan Dec. 27.

Only a month ago, the administration's attention was focused with single-minded intensity on forcing the quickest possible resolution of the hostage issue.

In an effort to break through that chaotic and blurred division of power and authority within Iran and make an impact on the revolution's principal leader, Ayatollah Ruhollah Khomeini, the United States was pushing as hard as it could to get the United Nations Security Council to impose economic sanctions against Iran.

The aim was two-fold -- to underscore to Iran its isolation by symbolically branding it an outlaw before the international community, and to increase its internal turmoil by subjecting the Iranian economy to a concerted trade and credit squeeze.

Senior administration officials also let it be known that they were considering an attempt to accelerate the effects of sanctions by clamping a naval blockade on Iran.

Then came the sudden and unexpected Soviet move into Afghanistan. As the administration entered the new year scrambling to piece together a strategy for responding to the new situation, the talk about blockades and other tough measures against Iran largely stopped.

The primary consideration, White House and State Department officials say, had become one of building confidence in the countries neighboring Iran and of enlisting their cooperation in plans to inject some kind of American military presence in the region.

One of the administration's best weapons in pursuing that aim, these officials add, is the widespread fear and hostility that the Soviet aggression has stirred among nonaligned countries, particularly those of the Moslem world.

But they also note, the strong anti-Soviet sentiment now sweeping much of the Persian Gulf region could swing back toward the United States if Washington instituted a blockade or other overt action against Iran. For that reason, the officials admit, the idea of a blockade has been put aside, at least for the near future.

Shelving the blockade idea was only the first step in the administration's change of direction toward Iran. In part, the change was dictated by such circumstances as the Soviet Union's decision to try to mend some of its fences in the Islamic world by voting the U.N. resolution on Iranian sanctions.

In the one major carryover of its pre-Afghanistan, get-tough approach to Iran, the administration has said it will attempt to apply economic sanctions unofficially with whatever help it can get from America's major industrial allies. Even that decision is known to have triggered misgivings among some key officials drafting an overall U.S. policy toward Southwest Asia.

These officials, most of them in the State Department, are understood to have argued that pushing sanctions now would, like the blockade idea, undermine U.S. efforts to project a more moderate and conciliatory image to Iran and other Islamic countries.

In the end, though, Carter and his top advisers are understood to have concluded that their past emphasis on the importance of sanctions left them no choice other than to continue along that route. Dropping the sanctions idea, it was decided, would have damaged Carter's credibility and exposed him to charges of backing away from the plight of the hostages.

For the most part, however, the pattern of U.S. approaches to Iran during recent days clearly has emphasized the carrot rather than the stick. In retrospect, the turning point appears to have been signaled Jan. 9, when a senior White House official, who earlier had been very active in describing Carter's mounting impatience over the hostages, emerged from a briefing for former Cabinet officers to say the president did not see "an early and successful conclusion" in the cards and was counseling patience and moderation over the hostage issue.

At the same time, the White House is known to have issued new ground rules for public statements on Iran by administration spokesmen. Instead of lumping all Iranian power groups together, the spokesmen were instructed to concentrate their fire on the militants holding the hostages by describing them as "Marxists" and "terrorists" working against the interests of the Iranian people and government.

That, administration sources admit, was a calculated attempt to drive a wedge between the militants and the mainstream of opinion within Iran. The idea, they say, is to undercut the militants' support among the masses in ways that will strengthen the hand of more moderate Iranian leaders seeking to persuade Khomeini that he should resolve the confrontation over the hostages.

In tandem with these public statements, senior administration officials at the White House and State Department, talking with reporters on a background basis, began stressing the contention that Iran's main cause for concern originates in Moscow, and that its desire for independence could be enhanced greatly by ridding itself of the hostage problem and turning a page in its relations with Washington.

Within the last week, this shift had become so pronounced that State Department spokesman Hodding Carter, in his Friday press briefing, was publicly emphasizing the U.S. commitment to Iran's territorial integrity and urging release of the hostages so that Washington and Tehran "would be better able to coordinate our concerns about Soviet aggression."

Whatever this new policy of talking softly and reminding Iran of the "red menace" at its borders will be more effective than the past hard-line approach is still a wide-open question, U.S. officials admit.

They cite the rising volume of statements by Iranian Foreign Minister Sadegh Ghotbzadeh and other Tehran officials condemning the Soviet presence in Afghanistan as grounds for cautious hope that Iranian moderates, who fear that their country may be next on Moscow's list, will be able to prevail on Khomeini to order the hostages' release and the repair of ties to the United States.

But, they also are quick to stress, it is likely to take a very long time before the United States has a clear idea of how the rapidly shifting events in and around Iran will affect the situation of the hostages, who today begin their 78th day in captivity.