President Carter said yesterday that the effort to free the 52 American hostages "looks better," but he added that he could not "predict success" for his administration's frantic, last-ditch effort to achieve an agreement with Iran during the final week of his presidency.

Carter's comment during a brief exchange with reporters came as administration sources said the United States is essentially waiting for Iran's reaction to a U.S. proposal for breaking the hostage deadlock before the president turns his office over to Ronald Reagan next Tuesday.

"It looks better, but I can't predict success," Carter said. "That depends on them [the Iranians]. We've made them a reasonable proposition." d

He didn't elaborate. However, informed sources have said that the United States hopes to win Iran's consent for a legally binding, international agreement that would set the terms for freeing the captives in exchange for a phased return of the frozen financial assets of Iran held by this country.

According to the sources, the United States hopes for an executive agreement that would be signed before Tuesday by Carter and either Iran or Algeria, which has been the intermediary in the indirect negotiations and which might be designated to act on Iran's behalf under the plan.

Such an agreement would represent a public, legal commitment by the U.S. and Iranian governments to abide by terms still being negotiated. In effect, it would mean Iran's agreement to release the hostages even though Carter, because of legal problems, can restore only a portion of the frozen assets to Iran before time runs out on his presidency.

However, an executive agreement such as that proposed by the administration would commit the United States to deliver the balance after dealing with possible legal challenges in U.S. courts by American corporate and individual claimants who have filed suits against Iran.

The sources said an executive agreement or, in the alternative, a unilateral executive order issued by Carter, theoretically could be repudiated by Reagan. But, they added, that would be unlikely, especially in the case of an agreement signed by both sides, because it would mean going against an international commitment made by a president on behalf of the United States and thus would violate the tradition of continuity in conducting the government's official business.

In Los Angeles, Reagan said his briefings during the last two days have given him reason to be more optimistic about the negotiations. But, repeating the caveat he issued last week, Reagan added: "I hope and pray and I think the president is negotiating on a basis that we can all agree to. On the other hand, I don't think anyone should be asked to sign a blank check."

Although the Iranians have made encouraging noises about the possibility of an imminent solution and have posed a long list of questions about the U.S. plan, administration sources stressed anew yesterday that there is no sign of whether Tehran will accept such an agreement.

For that reason, Deputy Secretary of State Warren M. Christopher, who has been in Algiers to expedite dealing with Iran through the Algerian intermediaries, delayed his departure for another day. State Department officials said there was no set time for his return her, and the expectation is that Christopher will wait in Algiers until Iran responds.

Christopher met yesterday with Algerian President Chadli Benjedid, but State Department spokesman John Trattner said the purpose of the meeting was to express thanks for Algeria's assistance. Trattner said the meeting "does not signal a breakthrough" or other dramatic event and that the administration's past statements about "serious differences" in the negotiations are still operative. There was speculation that the Iranian response might not be sent to Algiers before Friday, after the Iranian parliament completes work on bills authorizing third-party arbitration of disputed financial claims between Iran and the United States and nationalizing the wealth of the late shah and his family.

Friday is Carter's deadline for an agreement while he is in office. If Iran waits until then to respond, it could result in a down-to-the-wire finish that would see efforts to settle the hostage issue proceeding right up to the moment next Tursday when Reagan takes the oath of office.

In the meantime, other problems apparently await resolution -- chief among them the need to deal with Iran's demand for return of the late shah's wealth in this country and agreement on the amount of the assets held by the United States. Iran claims its frozen assets total $14 billion; some sources have said that preliminary U.S. estimates place the figure at $9.5 billion, while others contend that neither side is sure of the correct figure.