The Shah of Iran said last night his country would takee an active role in trying to keep oil prices down despite the fact that President Carter gave him no assurances that the United States would sell him all the weapons he wnats.

The Shah made the disclousure at a news conference in Blair House across the street from the White House, where he and President Carter concluded two days of talks while hundreds of anti-Shah demonstrators protested his visit.

Shah Mohammed Reza Pahlavi said this is a result of his meetings with Carter, he had changed his mind on the issue of world oil prices that will be decided when the 13-member Organization of Petroleum Exporting Countries, meets Dec. 20 in Caracas, Venezuela.

Before his discussions with Carter the Shah related "we were neutral" on the question of all prices." But after persuing the world economic situation, we came to the conclusion to give you a break.

The shift marks a major change in Iran's oil prices posture in past OPEC meetings it has been a "hawk in seeking large price increases. Last year, for instance, it favored 10 per cent increase, while Saudi Arabian opted for a 5 per cent increase.

Asked if he would support a price freeze for an entire year, the shah replied, "I wouldn't oppose it." Asked if Iran would offer such a proposal at the OPEC meeting, he answered, "I would say yes."

World oil prices are now set at $14.50 a barrel.

The shah confirmed that Carter told him he would make no decision on major new weapons sales to Iran without consulting Congress even though the President said the United States continues to support a strong Iran and considers its security a top priority for this country.

But the shah added that he is "not pessimistic" over the prospects of getting the weapons he wants. He said he understands that "there must be close cooperation with Congress" but added that "if they know the facts," the members will support Iran's requests.

His news conference capped a day that began with White House meetings with Carter and Energy Secretary James R. Schlesinger Jr., a luncheon given by Vice President Mondale and a tea with House and Senate members. The shah and his wife, Empress Farah, flew from Andrews Air Force Base to Paris last night.

Despite opposition in Congress, particularly in the Senate, to additional arms sales to Iran, the shah was understood to have described to Carter a long list of military equipment that he would like to buy.

Iran is the largest single purchaser of arms from the United States. During the last fiscal year it bought $5.5 billion of the $11.3 billion in weapons sold by U.S. firms, and since 1972 it has bought more than $18 billion worth of weapons from this country.

White House press secretary Jody Powell said Carter noted to the shah that the Pentagon and State Department are making studies, ordered by the Senate Foreign Relations Committee, of the military balance in the Persian Gulf region and of the ability of governments there to absort new military hardware.

Powell said Carter explained to the shah his and Congress' "concern about reducing arms sales abroad." Powell added that Carter also noted the "need to develop some type of dependable and predictable way of meeting the defense needs of Iran."

At his news conference the shah was asked if he had received an assurance of continued U.S. arms supply in return for keeping oil prices down.

"Not at all," he replied. "We are divorcing these two questions completely. We are trying to shop in your country for what we need and what you are ready to supply. That doesn't mean that if you do not supply [us], we will be helpless. We can get if from elsewhere."

The shah acknowledged that he asked Carter for 140 more F-16 fighter jets to add to the 160 he has already purchased from the United States.

Besides the F-16s, the shah is also seeking permission to buy 250 f-18 attack planes, about 100 military transport planes and three additional Boeing Airborne Warning and Control System (AWACS) radar planes. Earlier this year Congress forced Carter do delay the sale of seven AWACS planes to Iran, but after he resubmitted the $1.2 billion deal, Congress did not block it.

Yesterday, as Carter escorted the shah to a limousine after their 90-minute discussion, the President said they had discussed human rights, the issue which led to the violent protests Tuesday.

Carter did not elaborate but Powell said later that the President had noted the recent steps that the Iranian government has taken "in support of that ideal."

Powell listed the steps as changing Iranian criminal law to allow more due process considerations, opening prisons to inspection by the International Commission of the Red Cross, granting amnesty to about 1,500 security prisoners, and allowing foreign print and broadcast media to inspect jails.

Carter made clear "that this commitment to human rights is a fundamental and permanent part of U.S. foreign policy based on firmly held beliefs of the American people," Powell said.

He added that Carter told the shah that the United States has observed human rights conditions in countries around the world, including Iran, and would continue to speak out on them.

Asked if Carter is satisfied with Iran's progress on human rights, Powell said, "We have avoided throughout this process any overall judgement of any country."

Powell said the President and the shah agreed that "important progress" has been made toward a nuclear cooperation agreement between the two countries. Under the agreement, the United States could provide nuclear technology, including fuel and reactors to Iran, which would promise to use it only for peaceful purposes.

Powell said the two leaders hoped the agreement, which has been sought since 1974, could be completed "in the near future." The shah reportedly wants assurances that U.S. restrictions on the disposal of spent fuel would not make it impossible for Iran to operate its nuclear power plants at any future date. Iran plans to build 20 nuclear plants and wants to buy six to eight of them in the United States.