UNITED NATIONS, JULY 14 -- Iran's foreign minister charged today that the United States deliberately shot down Iran Air Flight 655, but Vice President Bush responded that the USS Vincennes fired in self-defense and he appealed to the Security Council for an end to the Persian Gulf war.

In an appearance intended to underscore his diplomatic experience and his campaign theme of vigorously defending American national interests, Bush took the U.S. chair at the opening session of the council debate on the July 3 downing in which 290 people were killed.

Foreign Minister Ali Akbar Velayati took the spotlight first with a 90-minute address that dwelt largely on details of the incident and called on the council to condemn the United States for "its inhuman massacre of innocent civilian passengers of Iran Air Flight 655." He said the disaster "could not have been a mistake," and he cited many contradictions in the U.S. accounts.

Velayati read aloud a transcript of communications between the Iranian pilot and the control towers at Bandar Abbas, Tehran, and Dubai, the flight's destination. The transcript appeared to confirm Iran's claim that the A300 Airbus was in the process of climbing to 14,000 feet seven minutes into the flight, just before it was hit by an American missile. Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff, had initially announced that the Airbus was descending before it was fired upon.

Velayati also said the transcript shows that the pilot told the towers that his transponder -- identifying the plane as civilian -- was turned on and functioning. Pentagon officials have said that the Vincennes picked up both military and civilian transponder signals, contributing to its misidentification of the Airbus as an attacking F14 fighter.

Acknowledging that Iran had shunned the council for seven years as favoring Iraq, Velayati suggested the debate over the airliner "may provide a litmus test to see whether this machinery can fulfill its responsibility."

Given the years of harsh rhetoric between the United States and Iran, diplomats friendly to each side said that both speeches adopted a relatively moderate tone. One western ambassador conceded that "the language Velayati used was technical, not violent; he was not seeking to exacerbate the situation."

Bush, in remarks added to his prepared text, rejected as "offensive" and "absurd" Iran's charge that the airliner attack was premeditated and said Velayati "knows that this tragedy was an accident." Bush said Iran must "bear a substantial measure of responsibility" for having permitted the airliner to fly into a combat zone. He also said Iran had acted in a "barbaric" manner by holding Americans hostage.

But the vice president echoed President Reagan's conciliatory approach by criticizing Iraq's use of poison gas in the war, conceding that both combatants must make concessions to reach peace and referring to Iran by its formal title as "the Islamic Republic."

In the wake of the incident Bush had said he would not apologize, but today he offered effusive expressions of remorse, saying, "Our reaction to this tragedy transcends political differences and boundaries. Of course we feel bad about this, of course we have compassion, of course we care."

In another remark added to his text, Bush said perhaps this Security Council debate "can be the catalyst to end the bloodshed and bring the peace."

The council adjourned until Friday after hearing the two protagonists. Behind the scenes, Council President Paulo Nogueira-Batista of Brazil continued to negotiate with both sides on a compromise text that could avert an American veto of a resolution condemning the downing. His spokesman said this could take the form either of a unanimous resolution or a statement issued on behalf of all council members. The talks were expected to go on into the weekend.

Velayati also hinted at Iran's willingness to pursue negotiations on the gulf war, saying that "such efforts should be continued." Velayati has been viewed as a hard-liner among Iranian officials and has tried to torpedo negotiating efforts by U.N. Secretary General Javier Perez de Cuellar.

In his address, Bush sought to divert attention from the July 3 incident to the issue of peace in the gulf. He defended the U.S. presence there as vital to maintain freedom of navigation until the war ends. He again accused Iran of having "played for time and maneuvered for diplomatic advantage." Bush noted that the Security Council adopted a resolution almost a year ago demanding an end to the fighting, but that Iran has not yet accepted it while Iraq has avoided discussion of practical ways to implement it.

Significantly, however, Bush did not restate U.S. demands for a resolution imposing an arms embargo on Iran for its refusal to end the fighting.

Today's appearance offered Bush an ideal opportunity to exploit a diplomatic mission for political advantage. Bush, who served as U.S. ambassador here from 1971 to 1973, returned to the Security Council for the first time and greeted old acquaintances.

Bush dismissed the political implications of the appearance as he arrived, saying his purpose was to defend "the fundamental foreign policy interests of the United States." Later, he refused to answer reporters' questions about the political ramifications.

The vice president listened as Velayati quoted from U.S. newspaper accounts -- including several from The Washington Post and The New York Times -- of contradictions in the administration's version of events. One of the points Velayati questioned was how the Vincennes could have been threatened by an F14 when these U.S.-made fighters are armed for attacking other airplanes, not surface targets.

Bush did not respond to details of the contradictions but took note of Velayati's newspaper sources and fired back that a free press does not exist in Iran. But, he added, in America "you can find comments to support any point you want" in the press.