President Carter has agreed to delay briefly U.S. moves toward seeking United Nations sanctions against Iran while U.N. Secretary General Kurt Waldheim completes "intensive discussions" with Iranian representatives, a White House official said yesterday.

The official, who asked not to be identified, said Carter postponed a decision on asking the Security Council for economic sanctions after Donald McHenry, U.S. ambassador to the United Nations, came to the White House yesterday with Waldheim's request for a delay.

But, the official added, the president's agreement "applies only to action relating to the United Nations and the Security Council." He and other administration officials stressed that a new recourse to the United Nations is only one of several options being considered by the United States to spur release of the 50 American hostages in Iran.

Since Tuesday, U.S. officials have been escalating their warnings of punitive responses, possibly including military movements, if the hostages continue to be held and are subjected to "public exploitation" before an international tribunal.

Although the administration has declined to specify what such responses might involve, it has been clear that the hostages must be released before the United States agrees to discuss in any way Iran's grievances against deposed shah Mohammad Reza Pahlavi and his past U.S. ties.

That was underscored anew yesterday by State Department spokesman Hodding Carter, who rejected as "blackmail" an Iranian suggestion that the hostages' situation might be improved if the United States holds some kind of official investigation into the shah's activities.

The suggestion that such an investigation could help resolve the 46-day crisis was made Tuesday by acting foreign minister Sadegh Ghotbzadeh in an interview with correspondents of The Washington Post in Tehran.

"For there to be conditions established which have to be met for the release of the hostages amounts to the accession to blackmail and will establish a precedent which will come back to haunt every country in the world," Carter said. "It creates nothing but blackmail and the victory of blackmail. The United States rejects that."

Carter said "it follows logically as night follows day" that Congress will look into the Iranian situation once the crisis comes to an end. But he denied that any deals are in the works to begin congressional hearings or probes before the hostages are released.

From the outset of the crisis, the administration has signaled repeatedly its willingness to talk about some forum -- either an international body like the United Nations or the congressional hearing process -- where Iran could air its grievances. But it also has insisted that it will resist any attempts to shift the focus of the dispute away from the plight of the hostages by giving Iran a hearing before they are freed.

The State Department spokesman echoed statements by White House officials that a number of options are being considered as the next U.S. step and said, "It would be misleading at this point to focus specifically on a specific option."

But, despite speculation in the past two days about the possibility of measures like a naval blockade, the main U.S. strategy at present is understood to aim at asking the U.N. Security Council to impose economic sanctions against Iran.

That course is understood to have been advocated by Secretary of State Cyrus R. Vance following his discussions last week with the leaders of America's principal European allies on concerted economic measures against Iran.

However, as the White House official revealed yesterday, a decision by Carter to seek a sanctions resolution has been held up temporarily by Waldheim's request. Waldheim, acting under the mandate of a Security Council resolution adopted unanimously two weeks ago, has been trying to open a negotiating channel with Tehran through Iran's new U.N. representative, Mansour Farhang.

U.S. sources privately are skeptical that Waldheim's efforts will produce any results at this time. But, the White House official said, in line with the administration's pledge to "pursue every available channel" to a peaceful solution the president "has made it clear we are willing to allow some additional time."

The official stressed, though, that delay is not "indefinite" and is expected to last no more than a few days.

U.S. movement in the Security Council also is understood to have been hampered by uncertainty about whether a sanctions resolution could win the required nine votes in the 15-nation council.

Questions also have been raised about whether the Soviet Union would veto a sanctions resolution, and Moscow has not responded yet to U.S. requests for clarification of its position. However, White House press secretary Jody Powell, asked yesterday about a Soviet veto, said a U.S. decision on asking for Security Council action would not be affected by the attitudes of any other government.

For the first time, the administration yesterday outlined the type of sanctions it is considering asking the United Nations to impose on Iran, the Associated Press reported.

"A whole range of sanctions are possible under the U.N. charter," Deputy Secretary of State Warren Christopher said. "It begins with the possibility of cutting off military shipments, the possibility of cutting off export credits, the possibility of curtailing or cutting off completely air and rail links."

Christopher said these options are "possibilities that will be under consideration if the United States decides at the United Nations to move to sanctions."

Meanwhile, medical sources said yesterday that the lymph gland cancer condition of the shah, who left the United States last Saturday for Panama, may be advancing rapidly. They cited the fact that his spleen has become enlarged alarmingly since his radiation treatment in a New York hospital for a cancerous swelling in his neck.

His doctors in New York said they were "pleased" with his response to the treatment. But, the sources said, when the shah was in San Antonio before going to Panama, the spleen enlargement was noted. The spleen is a common site of further spread of a lymphoma.

Dr. Benjamin Kean, the shah's chief doctor in New York, confirmed yesterday that a course of chemotherapy was started just prior to the shah's departure from San Antonio and is being continued in Panama.