President Carter, after a heated intragovernmental debate, has rejected a Pentagon plan to authorize the early sale of sophisticated F16 war-planes to South Korea.

Carter's decision was made on the eve of a mission to Seoul early this month by Defense Secretary Harold Brown, who had requested authority to tell the Koreans on that occasion that a "letter of offer" for the sale of about 60 aircraft had been approved. According to informed officials, Brown had committed the United States "in principle" as early as July 1977 to favorably consider supplying the F16 at some unspecified time.

The F16 has about twice the range and far greater maneuverability and electronic sophistication than any aircraft in the inventory of either North or South Korea. Thus its sale would violate Carter's self-imposed rule against introducing higher levels of military technology into regional disputes.

Moreover, opponents of the sale in the State Department and the Arms Control and Disarmament Agency argued that such a high profile U. S. gesture to South Korea might force the Soviet Union to respond by supplying up-to-date weaponry to North Korea. Apparently due to cool relation with Pyongyang. Moscow has not supplied new-generation war-planes or other major weaponry to its Korean communist ally for several years.

North Korea's most advanced combat aircraft is the Mig 21 interceptor, which was supplied by the Soviets in the mid-1960s. The newer Mig 23, which has been supplied in various versions to Bulgaria, Czechoslovakia, Egypt, Iraq, Libya, Syria and Cuba, has not been supplied to North Korea.

An authoritative Soviet diplomatic source, interviewed recently in Moscow, was asked what his country would do for North Korea if the United States supplied the F16 to South Korea. "We hope you will not put us into position to get into such rivalry," was the reply.

Another factor in Carter's recent decision was the impending turnover in the leadership of the Senate Foreign Relations Committee, which passes on overseas arms sales. A report to the committee last January by Sen. John Glenn (D-Ohio) and the late Sen. Hubert H. Humphrey (D-Miss) said any projected sale of the F16 to Seoul should be given special scrutiny in view of "the implications for an escalation of a Korean arms race."

The transition in several hey congressiona posts and the need to consult lawmakers was cited by Brown in his discussions in Seoul as the reason for postponing a decision to authorize the sale of the warplanes, informed sources said. Government officials in several departments expect Brown, the Joint Chiefs of Staff and Possibly the U. S. military command in Korea to make a major push for approval of the sale next year.

One new element in the situation then will be the position of retired Lt. Gen. George M. Seignious, who will become director of ACDA on Dec. 1 under a recess appointment. During his Army career. Seignious served as an officer in Korea and as chief of the Pentagon's weapons sales program and thus is believed by some to be likely to restrain or even reverse the agency's opposition to the F16 transaction.

The original decision to commit the in the wake of charges by Maj. Gen. was made at a time when South Korea was greatly upset over Carter's plan to withdraw U. S. ground forces from that country over five years, and United States to the sale in principle John K. Singlaub that the decision would lead to a new Korean war.

Government sources on all sides of the disputed sale say that not much discussion or debate about the military requirements or implications went into Brown's initial commitment, which is described as one of several measures taken in mid-1977 to placate Seoul. However, Pentagon and State Department sources said Carter was informed before the commitment was made.

Brown reportedly argued during the recent policymaking round that U. S. credibility is at stake in fulfilling the commitment "in principle," which has been reiterated in successive U. S. korean meetings. Pentagon officials also maintained that the Soviet Union will make its military supply decisions on the basis of its own interests, regardless of U. S. actions.

South Korea's request for "coproduction" (local manufacturer) of the advanced airplane, a request that also runs counter to Carter's arms sale policy, is unlikely to be approved even if the sales proposal is given the green light. The 60 F16s Korea wants including associated facilities and other costs, would cost about $1.2 billion. The planes could not be delivered before 1962.

The Carter administration, with congressional backing, has agreed to transfer about $800 million in supplies and equipment to South Korea in connections with the withdrawal of U. S. ground troops. In addition, as long list of military sales has been approved, including F4 Phantom jets, to upgrade Seoul's military capabilities.

North Korea is well ahead of Seoul in numbers of major weapons, including tanks and combat aircarft, but Seoul is believed to be ahead in the modernization and sophistication of its arms.

Seoul's latest weapon is a locally manufactured ground-to-ground missile that it claims can hit Pyongyang from the southern edge of the demilitarized zone. The missile is believed to have been technology and perhaps some parts of the Nike Hercules surface-to-air missile supplied by the United States.

The new missile, which was unveiled with a flourish in Seoul last month, is considered by U. S. officials to be of greater psychological than military importance.