The Carter administration and congressional leaders yesterday rebuked Rep. George V. Hansen (R-Idaho) for his one-man mission to Iran and his proposal for a congressional inquiry into the alleged misdeeds of deposed Shah Mohammad Reza Pahlavi.

Officials at the White House and the State Department said that Hansen's unauthorized venture into international diplomacy risked confusing Iranian authorities about U.S. intentions and the resolve of the administration to gain the freedom of the 49 Americans being held hostage in the U.S. Embassy in Tehran.

"It is not useful to confuse a situation already confused by raising a specter that there may be more than one voice negotiating or speaking for America," said State Department spokesman Hodding Carter.

Hansen traveled to Iran on his own last week and met with authorities there. On Sunday, he became the first American allowed to visit the hostages, seeing about 20 of them, whom he found in "relatively comfortable circumstances."

In a television interview from Tehran yesterday, Hansen called for "more talking and less saber-rattling" in the crisis, and said he will return to Washington soon to press for congressional hearings on the shah's rule.

The Hansen mission has exasperated administration officials, who view it as undermining their basic strategy in the crisis -- to keep attention focused on the plight of the hostages and to refuse to discuss other matters, including the shah's alleged crimes, until the hostages are freed.

White House press secretary Jody Powell said Hansen's activities have not been helpful, and that because his access to the hostages was carefully controlled he may not have gotten a completely accurate picture of their treatment.

Asked about Hansen's proposal for a congessional inquiry into the shah's alleged misdeeds, Powell said, "I doubt that the United States Congress is any more inclined to yield to blackmail than are the administration or the American people."

Powell's view was widely supported on Capitol Hill.

"He was out of bounds as far as a member of the House is concerned," House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said of Hansen. "As far as any deal he would make, he's not in a position to deal. That's for the U.S. government."

Hansen was also criticized by some fellow Republicans. Rep. Millicent Fenwick (R-N.J.) called his mission "dangerous" and "irresponsible."

In response to a direct request from Deputy Secretary of State Warren Christopher, House Foreign Affairs Committee Chairman Clement J. Zablocki (D-Wis.) pledged that no hearings on the shah's rule will be scheduled until the hostages are freed. Zablocki said many House members believe Hansen made a "grave mistake, and I agree."

However, a fellow Wisconsin Democrat, House Banking Committee Chairman Henry S. Reuss, said he might be willing to commit his committee to holding hearings on the shah if it would help free the hostages, but that he would not proceed with such an inquiry until the hostages are released.

Reuss said he took this position in response to a letter he received from Hansen asserting that it is "critically important that hearings be announced that will examine the situation in Iran and how it got that way."

While the administration was busily criticizing Hansen, it had little to say publicly yesterday about another figure in the Iranian crisis -- former secretary of state Henry A. Kissinger.

On Sunday, George Ball, undersecretary of state in the Kennedy and Johnson administrations, said that the shah might not have been admitted to the United States were it not for the "enormously obnoxious" pressure exerted by Kissinger. Kissinger has said he agreed with the decision to admit the shah, but denied playing a major role in bringing it about.

State Department spokesman, Carter reiterated that the shah, who is undergoing treatment for cancer and gallstones in New York, was admitted to the country on "humanitarian" grounds and not because of outside pressure from Kissinger or others.

The shah, whose return to Iran to stand trial on criminal charges is being demanded for the freedom of the hostages, reportedly will leave New York for Mexico this week.

Overall, administration officials painted a gloomy picture yesterday as the Iranian crisis entered its fourth week. The officials expect to gain U.N. Security Council backing for a resolution calling for the immediate release of the hostages. But while they believe this will increase the pressure and sense of isolation on Iran, they do not expect any immediate, tangible results from it.

Rather than sensing a "softening" of Iran's position, as reported by Hansen, Carter said at the State Department that he considers the situation to be "deteriorating."

And Powell said: "I cannot hold out some evidence of an impending breakthrough or startling new development."

President Carter, who returned from Camp David Sunday, spent yesterday at the White House. He had few publicly announced meetings.

At the State Department, some of the relatives of the hostages met with David Newsom, undersecretary of state for political affairs, and briefly with Secretary of State Cyrus R. Vance.

Asked if any of the relatives had privately criticized the decision to admit the shah to the United States, Hodding Carter said they had "indicated a variety of opinions" on that matter.

Meanwhile, the Organization of American States yesterday voiced its "deep concern" at the seizure of the embassy in Tehran and asked Iran to release the American hostages.

The OAS' political council said the actions "are in open violation of international law and could also upset the peaceful conduct of foreign relations."

It urged the Iranian government "to put an end to the occupation of the U.S. Embassy in Tehran, free all hostages and guarantee the security of diplomats there."

The resolution was unanimously approved by the 27-member council after a day-long debate.