CIA Director Stansfield Turner is expected to give me testimony on Capitol Hill this week to strengthen the Carter Administrations case for selling radar system to Iran.

Turner had previously expressed strong reservations about the $1.2 billion sale of the sophistioated flying electronics system to Iran on grounds that its technological secrets could leak too easily to the Soviet Union. His views were transmitted in a still-classfied letter to the General Accounting Office which was disclosed in The Washington Post on Thursday.

The CIA director's new testimony, to be delivered to a closed Senate Foreign Relations Committee hearing Thursday, will be strong influenced by a series of converations with Secretary of State Cyrus Vance late last week and National Security Adviser Zbigniew Brzezinski, it was learned.

Both Vance and Brezezinski are understood to favor the sale of Iran of the Airborne Warning and Control System (AWACS), which knowledgeable officials indicate stemmed from a broad, though never publicly detailed, arms transfer agreement reached by President Nixon and the Shah of Iran in 1972.

The Shan then expressed his desire of a U.S.-supplied air defense system, although AWACS was not specially mentioned.

Turner's reservations about security aspecis of the AWACS sale were cited by the GAO in a report that concluded the administration had failed to present an adequate justification or the sale.

In their conversations with the CIA director during the past fews days Vace and Brzezinski have been stressing the political aspects of the transaction, particularly the possible damage to U. S. relations with Iran should the sale be canceled - a course advocated by a influential group of senators.

The Iranians want to buy seven of the specially equipped Boeing 707 jets fitted with advance radar and electronics equipment produced by Westinghouse. At $125 million a copy the AWACS aircraft are the most expensive planes ever produced, even more than the B-1 bomber which President Carter canceled on June 30.

The airborne radar system, a subject of controversy since its conception, has already cost the U.S. government $2.4 billion. Congress has appropriated funds for acquisition of 28 of the planes.

It was originally conceived as a continental early warning system for the United States against a Soviet bomber attack and then justified as a tactical air defense system for NATO when the Soviet manned bomber threat to the United faded. But the NATO countries were not sufficiently tempted to buy it. Then the shad emerged as the prospective buyer and the Air Force was still eager to sell.

Congressional critics of the AWACS sale to Iran have privately expressed concern that Turner is being pressured into modifying his intelligence judgments by the combined pressure of policymakers in the White House, State Department and Pentagon.

This could revive charges, often heard during the period Henry A. Kissinger presided over the national security intelligence system, that the product of the CIA was being modified to conform with the political decisions of the policymakers.

Speaking of Turner's letter to the GAO, one intelligence official said that the CIA director "did it in the typical way he does things. He laid out both sides and a misinterpretation was created that he was against it (AWACS). He feels the final judgment is up to the policymakers.

The prevailing view within the administration is that the AWACS system is "essentially a defensive weapon, as one official put it, and that the dangers of its technology leaking to the Russians are outweighed by the political benefits of the sale of the shah.

It is also understood that while the system may have tactical benefits to the shah, it would also provide significant strategic intelligence dividends to the United States, deployed as it would be along the Soviet Unions's southern flank. Officials would not comment on this aspect of the case for the AWACS sale to Iron.

Critics have contended that in addition to the security danger cited by Turner in his letter to the GAO the system would require a force of American technicians in Iran, by some estimates 400 or more, to keep it operating.

The intelligence briefing books on the system contend, however, that a much larger ground team would be required to operate a ground radar system in Iran.

During meetings with congressional staff members last week, administration officials strongly defended the sale and at least one of them. Erich von Marbod, the Pentagon's liaison officer in Iran, was critical of Turner's letter to the GAO.

The Turner letter was drafted by Jack Thomas, a special assistant on the CIA director's intelligence community staff.

In a June 23 letter classified secret, the head of the Pentagon's Defense Security Assistance Agency, Lt. Gen. Howard M. Fish, wrote the GAO that the Iranians were "extremely effective" in protecting the security of American weapon systems sold to them.

The issue of AWACS to Iran appears likely to provoke a major debate in Congress on the arms transfer policies of the Carter administration at a time when they are still being formed. The principal Senate critics of the sale. Sen. Thomas Eagleton (D-Mo.) and John Culver (D-Iowa), have given notice that the AWACS issue is the ideal vehicle for that debate.