President-elect Ronald Reagan said yesterday that he would not provide "a blank check" to the Carter administration's diplomatic efforts to settle hostage-related issues with Iran. The comment may have added a new obstacle to the already complicated task of negotiating release of the 52 Americans by Inauguration Day, Jan. 20.

In a brief exchange with reporters, Reagan also spoke supportively of the Carter administration's efforts. But his refusal to sign "a blank check" -- a phrase he was volunteering for the second day in a row -- was expected to add to the doubts in Tehran about concluding an agreement now which would have to be carried out, in part, by the successor administration.

Reagan's comment, which was more equivocal than that which he made on the same subject during his fall campaign for the presidency, came as Deputy Secretary of State Warren Christopher conferred in Algiers with the authorized intermediaries in the idirect negotiations with Iran.

According to administration sources, Christopher's sudden trip Wednesday night was prompted by a message from the Algerians early in the same day raising "rather technical questions" about U.S. proposals for handling frozen Iranian governmental assets.

On Tuesday, the Algerians had cabled to Washington an Iranian request for clarification on the same points, which were described as details of the timing and methods for returning Tehran's money in connection with the hostage release. After receiving Washington's cabled reply early Wednesday, the Algerians requested additional information to make it possible for them to explain the complex legal and financial situation to the authorities in Tehran.

State Department sources said the Algerians withheld all or part of the Washington cable while awaiting a fuller explanation, rather than sending it on to the Iranians.

President Carter and his senior advisers decided Wednesday afternoon to send Christopher and several U.S. experts to Algiers to clear up the questions in person, according to the sources.

The officials said the Christopher mission is unlikely to offer substantive changes in the U.S. positions in the indirect negotiations, and they discouraged speculation that Christopher will urge the Algerians to depart from their limited role as intermediaries by recommending or even guaranteeing performance of the U.S. proposals.

The Iranian questions, according to sources familiar with them, were considered cause for hope in Washington because they requested additional details of the financial arrangements set forth in the most recent U.S. proposals. This seemed to suggest, without an explicit statement to this effect, that Iran was prepared to modify or abandon its insistence on financial "guarantees" that the United States has declared to be unreasonable and impossible.

There still remains a gap, which Christopher described on leaving Washington as "measured in large numbers," between the amounts of frozen Iranian assets that could be quickly provided to Iran when the hostages are released, and the sums that Iran would like to have.

The United States is seeking to explain to the Iranian authorities, through the Algerians, that as additional billions are added to an "escrow account" in Tehran's name, additional legal problems would be created that could delay implementation.

There is yet no suggestion of a shift in the Iranian position on the wealth of the late deposed shah, Mohammed Reza Pahlavi, according to U.S. sources. But unless Iran changes its demands on this point, there is no chance for an agreement, the sources said.

In Tehran, a four-man Algerian diplomatic team continued talks with Iranian officials on the terms for settling the hostage-related issues, dividing its time between the Algerian Embassy and the Iranian prime minister's office. The intermediaries declined to comment on the progress, or lack of it, in the talks.

Tehran Radio, meanwhile, continued its attacks on the U.S. president-elect. A radio commentary said Reagan's "slogan of militarism" meant he was doomed to meet the same ignominious fate as Presidents Nixon and Carter.

The president-elect made his comments about the settlement terms as he left the State Department after the first meeting of his prospective Cabinet.

Asked by reporters if he would carry out an agreement reached between Carter and the Iranians before Jan. 20, Reagan first replied that the question was hypothetical. Then he added:

"I'm quite sure that any agreement would be one that, yes, I could carry out.

"On the other hand, I don't think anyone should be asked to sign a blank check and so I can't give you an unequivocal yes.

"I can tell you that I am confident that the president is working toward an agreement that does preserve the honor of our country and that is aimed at trying to get those people home, which we all hope he'll be successful in doing."

As he left Blair House Wednesday night, Reagan had also been asked if he automatically would implement terms with Iran that were concluded by Carter. His response at that time was, "I would have to look at that situation . . . I do not want to write a blank check."

Last Sept. 12, in his most substantive campaign statement about the hostage issue, Reagan warned Iran not to delay release of the Americans in hopes of obtaining a better deal from him. "I also pledge that if elected I will observe the terms of an agreement [between the Carter administration and Iran]," he said.

As his airplane was being refueled in Oklahoma City later yesterday while en route to California, Reagan suggested that Christopher's trip to Algiers is grounds for optimism. "At last we might be getting someplace. . . . There must be something cooking," he told reporters.