Behind the ambiguity and shadows they have sought to place around their most recent public and private exchanges on the American hostages, Washington and Tehran appear to have only renewed a complex diplomatic and political game for playing for time.

Despite the officially encouraged optimism in Washington during the past weekend and President Carter's nonconfrontational dawn press conference yesterday, the flurry of the past week does not appear to have contributed significantly to a final release of the estimated 50 hostages held at the U.S. Embassy since Nov. 4.

The one specific diplomatic result of the exchanges between Carter and Iranian President Abol Hassan Bani-Sadr has been Carter's decision to pull back from last week's threat to impose new sanctions against Iran.

All other aspects to the exchange appear to have been undercut, as have previous release attempts, by the continuing split between Bani-Sadr and Iran's revolutionary leader, Ayatollah Ruhollah Khomeini, who has yet to give any sign that he favors transfer of the hostages to government control. Bani-Sadr had dangled the transfer, which the United States was seeking as the first step toward a release, in return for Carter's pulling back on sanctions.

Reports reaching Washington suggest that Bani-Sadr at best was proposing a fig-leaf arrangement that would have involved moving Iranian Revoluntionary Guards into the captured embassy to share custody with the militants holding the Americans. A decision on release would have to be approved by parliament, which is still not fully elected, as Khomeini repeatedly has said.

Why the White House chose to put much faith in this proposal now, after similar proposals had failed, is one of the most mysterious aspects of the affair. Whatever their intentions, however, Bani-Sadr and Carter managed to gain valuable time for each other.

Carter's pullback has probably brought Bani-Sadr more time to work for an ultimate release of the hostages. And the confusing sequence has kept Carter's handling of Iran's moving target for the political foes in this season of political primaries.

As they carefully leaked it to reporters last week, Carter administration officials conceded that the sanctions threat was largely a symbolic gesture in economic and diplomatic terms at this point.

But the symbolism created a major political problem for Bani-Sadr, who has been telling visitors for months that such a confrontational move by Washington would reduce his room to maneuver to find a solution that Khomeini could present as acceptable to public opinion.

The White House does not acknowledge that second thoughts about Bani-Sadr's political standing had anything to do with Carter's dropping of the sanctions ultimatum contained in at least two separate communications Washington directed at Tehran last week. Reporters here had been told that assurances from intermediaries that Khomeini was finally on board for a transfer of the hostages produced Carter's return to restraint yesterday.

Those assurances appeared to be seriously undercut when Khomeini resolutely refused to talk in a major speech about the possibility of transfer. Carter and Bani-Sadr then chose to talk past each other in their public declarations, picking and choosing those parts of the other's condtions and statements that played best with their own domestic audiences.

No breakthrough appears to have been gained. But the exchange has kept the ball in the air for a crucial week and brought the Iranian parliamentary session on the hostages that much closer. And perhaps for the first time the apparently competing political needs of Carter and Bani-Sadr have clearly intersected.