President Carter yesterday withdrew for 30 days his offer to sell seven expensive and sophisticated flying radar systems to Iran, thereby avoiding a head-on confrontation with Congress over an issue he clearly could not win at this time.

Carter's decision came only hours after the House International Relations Committee, in a surprise 19-to-17 vote, dealth him a major setback by approving a resolution to block the sale.

Senate Majority Leader Robert C. Byrd (D-W. Va.) interrupted a Senate filibuster to announce Carter's decision, while, elsewhere in the Hill the Senate Foreign Relations Committee was preparing to vote behind closed doors on a Senate resolution to block the proposed sale.

The Senate resolutions, sponsored by Sen. John C. Culver (D-Iowa), had the vigorous support of Byrd and Sen. Hubert H. Humphrey (D-Minn.), chairman of the Foreign Relations subcommittee that has held several days of hearings on the sale. After Byrd's announcement, the committee canceled the vote, which was expected to favor the resolution.

The legislators who led the opposition to the $1.2 billion sale of seven Airborne Warning and Control Systems (AWACS) - a plane even more expensive than the $100 million-a-copy B-1 bomber - immediately hailed Carter's decision.

"I'm pleased by the President's decision," said Culver. "It was a wise decision. It does acknowledge the serious congressional reservations about the proposed sale."

"I'm happy," said Rep. Gerry E. Studds (D-Mass). sponsor of the House resolution. "The President may not think so, but I think it's a victory for his policy."

Studds' reference was to an arms sale control policy Carter announced May 19, in which he pledged that the United States would not be the first nation to introduce into a region new technologies that create new military capabilities.

Much of the opposition to the idea of selling AWACS to Iran, a nation which is already one of the biggest purchases of American arms, stemmed from the proposal's apparent violation of Carter's policy.

But in a statement released late yesterday by the White House, the administration indicated that Carter bowed not to any of the several substantive policy questions that have been raised aboutt he sale, but instead to a procedural question that had to do with the amount of time Congress has had to debate the sale.

Carter announced the offer to sell WACS to Iran on July 6. Under a never-before-used 1973 law, Congress had 30 days - or until Aug. 5 - to approve resolutions in both houses to prohibit the sale. Otherwise, the sale would have gone through automatically at the end of the 30 days.

Congressional leaders, led by Byrd, have argued strongly in the past week that Congress will not have enough time to debate the issue fully by Aug. 5, because of an already crowded calendar for the week remaining before the August recess, which begins Aug. 6.

Yesterday's White House announcement said Carter will resubmit the offer the day Congress comes back from its recess on Sept. 7. Congress will then have another 30 days, or until Oct. 7 to take action if it still wishes.

In a letter written to Humphrey yesterday, Carter said he is prepared to accede to Humphrey's request of Wednesday for six new assurances that the sale of the latest in U.S. radar technology would not jeopardize U.S. national security.

Humphrey asked for the assurance in a letter warning that the Subcommittee on Foreign Assistance had serious reservations about the sale. The assurances include the removal from the planes to be sold to Iran of some sensitive communications equipment, U.S. monitoring of Iranian security and a stipulation that AWACS would be used only for defensive purposes in Iran.

The major-arguments against the sale have been that AWACS could fall into the hands of the Soviet Union, giving that country technology it does not now have, and that it is destabilizing because it can be used for offensive purposes.

Humphrey and Byrd have reportedly committed themselves to supporting the AWACS sale when Carter resubmits it in September in the modified form. Their support would leave opponents of the sale without two of the most potent Senate forces they recruited in the current effort to stop the sale.

The White House statement said "The President is confident that once Congress fully discusses the proposed sale, and assesses the assurances we have provided . . . the sale will receive favorable congressional review."

Before hearing of Carter's intention to resubmit the offer in September, Culver, whose dramatic testimony in the House committee yesterday reportedly influenced several critical swing votes, said he expected the President to study possible alternatives to AWACS before making a new offer.

Backed by a General Accounting Office report, Culver has maintained that there are cheaper ways than AWACS of providing for Iran's air defense - ways that would not jeopardize as signifcant a technological edge as AWACS is for this county.

AWACS is a modified Boeing 707 jet, containing the most sophisticated available radar equipment, built by the Westinghouse Corp. It provides the best low-level radar detection available, but is so expensive that it has been turned down by every potential buyer - including NATO - except Iran. The Iranian emabssy had no immediate comment on the delay.

After unsuccessfully urging the House committee not to block the sale, Secretary of State Cyrus R. Vance told reporters a delay "would give an impression of a lack of constancy in a course of action in which we believe."