In his most extended report to the American people on the Iran crisis, President Carter made his bid last night to head off demands for precipitate military action, even while keeping all his options open.

With a measured, determined tone and carefully chosen words, Carter left the possibility of future retaliatory measures hanging in the air, even as he refused to discuss them directly or set deadlines for the "preferable" peaceful solution.

Initial reaction from his competitors for the highest office was favorable. Republican presidential hopefuls John B. Connally and Sen. Bob Dole (Kan.), in almost the same words, said the country has "but one president" at a time.

"Now's the time to rally behind him to show solid front to Iran and to the world," said Connally. "You will hear no denunciations of past mistakes" at this time and see no exercises in "personal diplomacy" by him, Dole pledged.

Sen. Edward M. Kennedy (Mass.), the leading Democratic challanger, said while on a tour of northern Iowa that Iranians must understand that "the American people speak with one voice on this question."

The growing impatience that Carter sought to stem is scheduled too be expressed in tangible form this morning at a news conference to announce a call by 54 House members -- about one-eighth of that body -- for Iran to be given a firm deadline beyond which "selective" U.S. military action will be ordered.

According to Rep. Samuel S. Stratton (D-N.Y.), one of the sponsors of the proposal, the 49 Americans in the U.S. Embassy in Tehran could be held hostage "for a year or even two years" unless a deadline is set. Stratton said his House resolution does not specify what deadline should be set, or what military action should be taken.

By unanimous vote yesterday, both the House and the Senate demanded "an immediate, safe and unconditional release" of all the hostages and called on the United Nations Security Council to take "all measures necessary" to achieve that end. Congressional leaders describe the measure as an expression of national unity.

As Carter made clear last night, the main U.S. hope for a peaceful outcome is tied to the Security Council debate on Iran scheduled to begin Saturday night. The U.S. strategy is to try and use the debate as a forum both for demonstrating to Iran that it has no support in the world community and for exploring face-saving ways for Iran to back away from a showdown.

The continuing political chaos in Iran -- underscored anew yesterday by the ouster of Abol Hassan Bani-Sadr, the acting foreign minister who agreed to the U.N. debate -- has left unclear whether Iran is willing to cooperate in what Carter called "this exercise of international law."

Whether Iran now will boycott the Security Council meeting probably will not become known until the debate is almost ready to begin.

Specifically, the United States expects that the 15 council members -- including those from communist and Third World countries -- will unite behind a resolution calling for release of the hostages as an obligation of international law. In the U.S. view, that would be the most dramatic demonstration to date that Iran has no diplomatic backing for its actions.

In addition, if Iran is willing to take advantage of the forum being offered, the United States is prepared to let the Iranians air their grievances against Washington and the deposed Shah Mohammad Reza Pahlavi at great lengths during the debate. Such an opportunity, U.S. officials hope, could help provide Iran a psychological catharsis that might make it more flexible.

Finally, if the Iranians decide to send a representative with authority to negotiate on the Ayatollah Ruholah Khomeini's behalf, the United States hopes it will be possible -- through the intermediary offices of U.N. Secretary General Kurt Waldheim and non-aligned countries -- to strike a deal that would couple release of the hostages with appointment of an international commission to investigate the shah's alleged crimes.

Carter held out this possibility at his news conference, noting that complaints against the shah "can be pursued under international law" and indicating U.S. willingness to explore different ways it could be done. But, in a pointed reaffirmation of his insistence that the hostages first be freed, he asserted that "no international forum" would listen to Iran's complaints while that country continues to violate international law.

Between now and the unwinding of the U.N. debate, a number of things are expected to occur that could make the atmosphere more conductive to such a deal. These include the anticipated imminent departure of the shah from the United States, the end of the emotional, passion-inflaming Moslem religious holidays now being celebrated in Iran and the completion of Iran's Dec. 2 referendum on Khomeini's powers under a new constitution.

In the end, though, the changes for a peaceful solution through the U.N. channel will depend on the still unanswered question of Iran's willingness to pay attention to world opinion and cooperate. Should Iran respond negatively, the U.N. option will fall, and Carter might have to start coming to grips with tougher action that he kept in the indefinite future last night.

According to a report from the Los Angeles Times, Treasury Secretary G. William Miller, enroute home from a visit to Saudi Arabia, Kuwait and the United Arab Emirates, said the use of U.S. military force against Iran could do "irreparable harm" to American hopes for continued oil production by neighboring Arab states.

Miller said leaders of the three countries he visited, while wanting the American hostages released, oppose any U.S. military action. "There is a deep desire to avoid force and violence for fear it will set off a chain reaction," Miller said.

On the 25th day that the American hostages were being held in the Iranian capital, in the greatest personal test and political ordeal of his presidency, Carter appeared tired and drawn as a result of the crisis.

Nonetheless, he repeated with powerful effect his unrelenting determination to see that "every single American" is freed without harm. He employed such strongly charged words as "courage," "honor" and "blackmail" in a manner that was firm but not fiery.

Near the end of the unusually long opening statement, Carter appealed for passage of the energy bills he has sent to Congress, declaring the nation is "vulnerable to being held hostage by our overwhelming dependence on oil from foreign counties."

This was an old and familiar theme. Less than two weeks after taking office, wearing a sweater in a fireside address from the White House on Feb. 2, 1977, Carter called for national sacrifice to deal with the energy shortage that plagues the United States and most of the rest of the world. CAPTION: Picture 1, Reporters clamor for President Carter's attention last night at White House news conference occupied entirely by questions about the Iranian crisis. By Frank Johnston - The Washington Post;

Picture 2, Carter: "I never forget for one moment that I'm awake about the hostages whose lives basically depend on me." By Frank Johnston - The Washington Post