President Hafez Assad lashed back yesterday at western governments that have accused Syria of supporting terrorism and vowed that he would not be intimidated by what he described as "threats" from the Reagan administration.

Adopting an unyielding tone during a lengthy interview here, the Syrian leader suggested that "the verbal bombs" directed by President Reagan at Syria and the U.S. bombing of Libya last month have frozen U.S.-Arab cooperation on a wide range of issues, including Syrian efforts to free Americans taken hostage in Lebanon.

The raid on Libya "won a lot of hatred" for the United States in Arab nations and across the Third World, said Assad, who is an ally of Libyan leader Muammar Qaddafi. "In every way, President Qaddafi is the winner and the United States is the big loser."

Assad disclosed in the interview that his government, which has an estimated 30,000 to 40,000 troops in Lebanon, had made "serious efforts" to win the freedom of the Americans, believed to number four, being held by Islamic extremists. "The U.S. administration knows that we previously expended much effort on this matter," he added.

"But no one can do anything when the U.S. administration is carrying the hammer of war . . . . It is very difficult to handle the question of the hostages in isolation from the U.S. political stands."

Speaking in Arabic, with his remarks translated into English by his interpreter, the Syrian leader made these other key assertions:

*Neither Syria nor Israel has undertaken any unusual troop movements on the ground in recent days despite reports of growing tensions. The tensions now seem to be lessening, Assad said.

*No terrorist actions abroad will be allowed from Syrian territory. But Assad indicated he would not move to restrict the "cultural and political" activities here of the renegade Abu Nidal Palestinian group, which American officials have identified as a major source of terrorist attacks against Americans and West Europeans.

*Syria will not involve itself any deeper in the "quagmire" of Lebanon, and will not seek to impose the tripartite power-sharing agreement it got Christian, Shiite Moslem and Druze leaders to sign late last year. The accord has been blocked by resistance from Lebanese President Amin Gemayel and, according to Assad, from the United States.

*Relations with Iran are good. But Assad hinted at possible strains by noting that he had sent his foreign minister to Tehran this month to reemphasize Syria's concern about the Iran-Iraq war spreading to other Arab countries in the Persian Gulf. Iran's occupation of Iraqi territory around the old oil-exporting port of Faw in a continuing offensive has embarrassed Syria, Iran's only important ally in the Arab world.

The embarrassment stems from Assad's claim to be the principal spokesman for the liberation of Arab land now claimed or occupied by Israel. The occupation of Iraqi territory by non-Arab Iran undercuts Assad's position.

The 55-year-old Assad, who has ruled Syria with an iron grip since seizing power in a military coup in 1970, has become the center of an international storm in recent days as British, West German, Israeli and American officials have said that Syria appears to have provided support for terrorist operations mounted in London and West Berlin. Pressed by journalists, President Reagan said at the Tokyo summit this month that he would consider ordering military strikes against Syria if evidence showed a Syrian connection to terrorist operations.

Seated in a green velvet chair and speaking in a soft, slow voice for most of the interview, Assad gave little outward sign of being perturbed by the storm of criticism and tensions swirling around him.

His long, thin face frequently broke into an off-center smile that hooked upward as he told an anecdote to illustrate a point or as he expressed dismay at U.S. policy. Although aides had asked for questions in writing before the interview, Assad quickly discarded the list and with confidence fielded questions spontaneously.

Felled by a heart attack two years ago, he gave no indication of tiring during the 3 1/2-hour discussion with four journalists. But his thinning hair has noticeably grayed in recent years, and he appeared to need to conserve his energy more carefully than in the past. He paused only once during the interview, which began shortly before sunset, and that was to break the daylong fast Moslems observe during the month of Ramadan by taking a cup of broth.

Assad left no doubt that he wanted to use the interview to respond to what he presented as unjust accusations and dangerous threats from western officials, and particularly from the Reagan administration. Until now, he noted, he had not publicly responded.

Seen by both Henry Kissinger and Jimmy Carter as a key interlocutor on the Middle East, Assad said that he had become "bitter and disappointed" over the Reagan administration's policy of alternately ignoring and confronting Syria.

He couched his bitterness at the deterioration of U.S.-Syrian relations in personal terms, whether speaking of Reagan's seemingly off-handed disregard of Arab leaders and Arab opinion, or of the Arab reaction to the April 15 attack on Libya.

Voicing disbelief that "a superpower would use a fleet of bombers and fighters to try to assassinate a head of state," Assad recalled that he had recently stayed as a guest in a house in Qaddafi's residential compound that had been destroyed in the American bombing raid.

"I know the house which was bombed. It was in the past the residence of Col. Qaddafi. Later it was converted to a guest house, and Col. Qaddafi moved to a nearby smaller house for a residence . . . . It seems that the American intelligence had thought it was still the residence of Col. Qaddafi and therefore destroyed it."

Assad's remarks appeared intended to emphasize that despite a series of reversals in recent months for Syria, he does not feel isolated or under pressure strong enough to make him drop his alliances with Libya and Iran or to change other policies.

The increasingly angry exchanges between Washington and Damascus over the issue of terrorism clearly rankled him, however.

U.S. officials in the past have not singled out Syria for the kind of repeated denunciations aimed at Libya under Qaddafi. Washington appeared to draw a distinction between the actions mounted out of Libya directed specifically at American targets, and Syrian-backed operations that concentrated on Syria's Arab opponents or on Israeli targets.

But accusations in the past two weeks that Syria helped supply explosives to a Jordanian arrested in London -- in a failed attempt to blow up an El Al airliner on April 17 -- have focused attention on Syria's role in terrorism. And they have shaken those American officials who felt Assad would keep Syrian operations under tight control, particularly in times of tension.

Although the would-be El Al bombing unfolded at London's Heathrow airport, American officials have pointed out that the London-Tel Aviv flight actually originated in New York and that more than 200 Americans were among the 340 passengers.

Vehemently denying that "the United States administration is entitled to level charges of terrorism against Syria," Assad maintained that "the CIA has a hand in every terrorist organization in the world."

Among the "terrorist" operations he attributed to the Reagan administration were the 1983 invasion of Grenada, the hijacking last year of the EgyptAir plane carrying the Palestinian hijackers of the Achille Lauro cruise ship, and support for an Israeli interception in February of a Libyan airliner carrying Syrian officials home from Tripoli.

Assad went on to deny specifically that Syria had been involved in the attempted El Al bombing in April.

"Although we wish all kinds of disasters to befall Israel, since we are enemies and in a state of war for 38 years -- and the Israelis wish the same for us -- we refuse to carry out such acts against civil aviation. We condemn the hijacking or exploding of civilian aircraft. Such acts are cowardly," he said.

Assad said that he had never met Sabri Banna, who as Abu Nidal heads a breakaway Palestinian group accused of carrying out attacks on Palestinian moderates, American tourists and others with the help and urging of Qaddafi.

"Abu Nidal is not in Syria . . . he does not operate anything in Syria. There is an office doing cultural and political work among the Palestinians, but those who are in Syria have nothing to do with terrorist acts," Assad said.

The presence of the office in Syria and the publication by the Abu Nidal group of a magazine here have become a symbolic test for the Reagan administration, which would like to see Syria close the operation down.

But Assad said he would not do this, and he denied that his troops in Lebanon could close down a terrorist training camp that Abu Nidal runs in the Bekaa Valley in an area under Syrian control. American officials assert the Syrians could easily close the camp.

"There is Syrian influence in Lebanon, but not Syrian sovereignty . . . . We do not interfere in their affairs or the affairs of the inhabitants . . . . We are not responsible for what happens in Lebanon. Moreover, the Americans, the British and the French were in Lebanon but could not prevent such things."

Much of the interview was devoted to a discussion of past and present Syrian efforts to gain the release of foreigners taken hostage in Lebanon by Islamic extremists who generally follow the line of Iran's Ayatollah Ruhollah Khomeini.

Those efforts triggered a warning this week from an anonymous caller in Beirut claiming to represent Islamic Jihad that attempts by Syria to gain freedom for the American hostages could result in their deaths. There were also unconfirmed television and newspaper reports in Washington this week that emphasized a new effort by Syria to get the hostages freed.

But Assad said Syrian efforts had been stymied by the April 15 bombing of Libya and other American political acts that had caused the small groups holding the hostages to break off contacts, and he gave no indication that a new effort had been launched since then.

"Our attitude in Syria toward these hostages has nothing to do with our relations with the American administration," Assad quickly added, "either negatively or positively. We shall do all that we can for their sake as we did in the past for the sake of others."

The American hostages -- Associated Press Beirut bureau chief Terry Anderson, the Rev. Lawrence Jenco of Catholic Relief Services, and Thomas M. Sutherland and David P. Jacobsen of the American University of Beirut -- reportedly are moved regularly between west Beirut and the Bekaa Valley by the Islamic Jihad group that asserts it is holding them. A fifth American, U.S. Embassy political officer William Buckley, is believed to have been killed by his captors, although no body has been found.

Assad said that Syria did not know the location or condition of the hostages, nor exactly who was holding them. Syria had opened contacts with Hezbollah, an Iranian-supported guerrilla group that is linked to Islamic Jihad, last year in an effort to gain the freedom of French and American hostages, the Syrian leader acknowledged.

In January, the Syrians believed they had reached agreement with Hezbollah on the imminent release of the French hostages, but the deal fell through at the last minute, leaving "misunderstandings between us and them. Until now, there are problems between them and Syrian forces in the area," Assad continued, confirming reports of clashes in recent weeks between Hezbollah units and Syrian troops in the Bekaa.

He said the clashes were not specifically related to the Syrian efforts to get the American hostages out, but were "byproducts, because when there is misunderstanding it may cause daily problems."

Assad characterized French President Francois Mitterrand as the western leader "most concerned" about hostages and still making "serious efforts" to get them released.

Despite his protestations of continuing interest in helping the hostages, Assad also made clear his resentment over what he described as a lack of official American gratitude for the Syrian role in freeing Americans taken hostage in the hijacking of a TWA airliner to Beirut last June:

"I do not think anyone else helped in that matter. Even the American administration was unable to do anything then to help those hostages."

Assad also mentioned in passing that Syria had played a role in obtaining the release in July 1983 of David Dodge, acting president of the American University of Beirut, from captivity.

Such actions, juxtaposed with strong suspicions of Syrian involvement in support of terrorism, have produced an ambivalence about Assad among many western analysts.