Iran's new foreign minister, named yesterday after Ayatollah Ruhollah Khomeini fired Abol Hassan Bani-Sadr, said today: "I'll try to assure everyone" that the 49 hostages at the U.S. Embassy "will be treated well."

Foreign Minister Sadegh Ghotbzadeh, in his first interview, called for an end to warlike rhetoric but added that he believes President Carter lied . . . concerning the hostages' conditions of detention."

Although Ghotbzadeh said he had not yet studied Carter's new conference remarks, he said, "If the Americans do not escalate, I believe things will stay the same as they are."

While President Carter indicated earlier this week that the prisoners were not being treated well, Rhotbzadeh said, "I think they are in pretty good conditions. The only thing they haven't had is liquor."

Ghotbzadeh said yesterday on taking office as the third foreign minister in as many weeks, that no decision had been made yet on whether he should attend a United Nations Security Council session scheduled for Saturday to consider the U.S.-Iranian crisis.

Today, in cautioning against warlike rhetoric -- "any inflammatory words are damaging to the entire situation" -- Ghotbzadeh singled out Zbigniew Brzezinski, Carter's national security adviser, for special attention.

"If I were Brzezinski, I'd sit down and try and calm the situation," Ghotbzadeh said. "I would stop thinking and talking like warmongers to collect votes."

He refused to be pinned down about his strategy or even tactics until he had conferred later today with the ousted Bani-Sadr.

However, he suggested that the avenue of congressional hearings into the shah's alleged misdeeds as a way out of the deadlock was "probably a burned card."

"Carter has burned the card by putting pressure on Congress. . . . They didn't have to react so harshly."

In military developments, the governor of the Persian Gulf port of Bushehr announced that foreign helicopters were banned from overflying the Straits of Hormoz and that tough security measures were in force at the principal oil loading port on Khark Island.

The newspaper Etelaat said that the government had warned all airplanes to stick to regular routes and destinations and avoid changing altitudes or risk being shot down.

A U.S. Navy plane used to jam anti-aircraft firing systems crashed into the Indian Ocean yesterday while flying on patrol off the aircraft carrier Kitty Hawk, officials in Washington said.

Navy officials said there was no indication that the plane went down because of hostile action. A search for the four-man crew was under way.

[The Kitty Hawk is part of the flotilla of 19 ships now in the waters off Iran.]

[The Soviet Union in the last week increased its naval presence in the Indian Ocean from about 12 to 15 ships, half of them combat vessels, according to Pentagon spokesman Thomas B. Ross. Ross said on Tuesday that 15 ships "is not an abnormal number" for the Soviets. They have had as many as 20 ships in the Indian Ocean at one time in the past.]

High Iranian naval sources told reporters that 15 Soviet warships have been sighted "on our radar" in the Gulf of Oman near the Strait of Hormoz, the 40-mile-wide channel through which passes much of the non-Communist world's oil.

The change in leadership at Iran's Foreign Ministry involves two revolutionaries who have remained bitter rivals during more than 10 years' exile in France where both worked for Khomeini's return to Iran.

Ghotbzadeh, 42, is a bachelor given to well-cut Western clothes. For years he badgered foreign politicians and newsmen on Khomeini's behalf.

Son of a merchant family, he left Iran in the early 1960s and says he has studied languages at Georgetown University's foreign service school. He has said he was expelled from Georgetown in his third year after illness prevented him from completing courses. He said he was forced to leave the United States under pressure from Shah Mohammad Reza Pahlavi.

Ghotbzadeh, who retains his influential job as radio-television chief, said he would decide about attending the Security Council meeting after seeing Ban-Sadr today.

Bani-Sadr retains his responsibility for economic and financial affairs, a Revolutionary Council spokesman said last night. A news broadcast pointedly referred to Bani-Sadr as an "acting," rather than full, minister.

On the midnight television news Ghotbzadeh said his appointment "will not change the framework of basic foreign policy" which "is the same as described" by Khomeini.

"We will follow that carefully," he said. At face value, Khomeini's last major foreign policy statement Tuesday vetoed Iranian participation in the Security Council debate and scutled a variety of Iranian and foreign-backed compromise solutions for the current crisis.

Bani-Sadr's dismissal from the Foreign Ministry, officially announced after Khomeini met the Revolutionary Council in the holy city of Quom, did not come as complete surprise.

As early as Monday reports had circulated of his resignation. They were touched off by the late Sunday night denial of a formal announcement made only hours earlier that he would be leaving to attend the United Nations Security Council session.

Informed sources said that Bani-Sadr had failed to clear the U.N. trip with Khomeini. Ibrahim Yazdi, his predecessor at the Foreign Ministry, fell from grace for a similar reason, after an October meeting in Algiers with Brezezinski.

Yesterday, Tehran Radio announced that Bani-Sadr would be leaving Friday for the United Nations.

But within hours the radical Islamic students holding 49 Americans hostage at the U.S. Embassy denounced the Security Council as an American-controlled "plot-setter."

The students, who increasingly seem to be calling the shots here, said "it is obvious that Iran's Islamic Revolutionary Council will not send any representative to the American Council of so-called Security."

Before returning to Iran from exile with Khomeini, new acting Foreign Minister Ghotbzadeh lived in Paris, where, associates say, he was not known for a devoutly Islamic lifestyle.

His Iranian passport was confiscated because of his activities as a leading opponent to the shah's regime and an organizer of Islamic Iranian students resident in Europe.

For years he carried a Syrian passport but in 1978, accompanying a correspondent for a French newspaper to interview Khomeini in Iraq, he used a Bahraini passport that caused him some difficulties.

Iraqi airport police in Baghdad were astounded that he had no knowledge of Arabic, Bahrain's official language, until the French newspaperman helpfully explained that Ghotbzadeh was part of Bahrain's large Iranian minority and spoke only Persian.

His tenure at National Iranian Radio and Television since the revolution has not endeared him to the staff, which he has purged, or to many Westernized Iranians angered by the disappearance of all American programs.

He has been criticized for driving around the poor districts of South Tehran in a locally assembled car while availing himself of a chauffeur-driven brown Mercedes 450 for his trips elsewhere in the capital.

In one of this last acts as foreign minister, Bani-Sadr yesterday defended his dealings with Rep. George Hansen (R-Idaho) who recently spent six days here.

He denied that any negotiations had taken place. "We though this gentleman is a Republican and is on bad terms with the Democratic Party," Bani-Sadr told the newspaper Ethelaat. "The Democrats owe the Republicans a Watergate."

When Hansen suggested a U.S. congressional hearing into the shah's alleged misdeeds, Bani-Sadr said he told him it was a good idea; go and do it."

Washington Post special correspondent Michael Berlin reported the following from the United Nations:

Members of the U.N. Security Council were stunned and somewhat paralyzed by the barrage of criticism emerging from Tehran and the abrupt dismissal of Bani-Sadr.

Without any official word on whether Ghotbzadeh would come here on Saturday, the council members, including the Americans, were left expressing hope that he would show up and determination that the debate would go on as scheduled.

Secretary General Kurt Waldheim said that the United Nations thus far has had no communications with Iranian authorities on Ghotbzadeh's participation.

The American ambassador, Donald McHenry, called the developments "discouraging but not surprising. I am still confident the Council will go ahead with its meeting." CAPTION: Picture 1, SADEGH GHOTBZADEH . . . replaces fired Bani-Sadr; Picture 2, ABOL HASSAN BANI-SADR . . . foreign minister for 3 weeks