President Carter sharply rebuked the Soviet Union last night for the coup in Afghanistan, accusing President Leonid I. Brezhnev of providing a "completely inadequate and completely misleading" response to U.S. protests.

Brezhnev "claimed that he had been invited by the Afghan government to come in and protect Afghanistan from some outside third-nation threat," Carter said in an ABC News interview. "This was obviously false."

The president's statement -- the first official assessment of Brezhnev's response -- represents a new low in deteriorating U.S. Soviet relations. Carter underscored the decline, saying the Soviet move into Afghanistan "has made a more dramatic change in my opinion of what the Soviets' ultimate goals are than anything they've done in the previous time that I've been in office."

He asserted that further U.S. action would be taken in response to the Soviet-backed coup in Afghanistan, but did not indicate what that might be.

Carter reserved his sternest criticism for Brezhnev. Asked whether the Soviet leader was lying, Carter replied, "He's not telling the facts accurately, that's correct." Carter sent Brezhnev a personal protest last Friday, a day after the Kabul coup took place.

Brezhnev's response was false and inadequate, Carter said, "because the person that he [Brezhnev] claimed invited him in, President [Hafizullah] Amin, was murdered or assassinated after the Soviets pulled their coup."

"It is only now dawning upon the world the magnitude of the action that the Soviets undertook in invading Afghanistan," Carter added.

Asked about the continuing impasse with Iran where 50 Americans have been held hostage at the U.S. Embassy since Nov. 4, Carter replied that he was "angry and impatient," but added that he could not set a deadline for the hostages' release.

"For us to peremptorily cause bloodshed or start a war in Iran and in that entire Persian Gulf region -- just to show that I am brave or courageous or forceful or powerful -- would be exactly the wrong thing to do for the hostages and for our long-range interests," Carter said.

Shortly before the president issued his rebuke to Brezhnev, the State Department made public new evidence of Russian involvement in the Afghanistan coup by accusing the Soviet Union of broadcasting "pre-recorded" statements by Afghanistan's "new puppet president."

State Department spokesman Hodding Carter asserted that radio broadcasts announcing Thursday's coup were tape recorded in advance by the new Afghanistan president, Babrak Karmal, and transmitted from southern areas of the Soviet Union, rather than by Radio Kabul.

Informed U.S. sources said the broadcasts came from the Soviet city of Termez, just north of the Afghanistan border.

Hodding Carter charged that the radio broadcasts were clear evidence that plans for the Afghanistan coup were "well in train as a matter of policy" set by the Soviet Union.

The State Department did not disclose its basis for the assertion that Karmal's coup announcement was tape recorded in advance and broadcast from the Soviet Union, but spokesman Carter said the report was based on "reliable indications."

Informed U.S. sources noted, however, that American diplomats and U.S. monitoring services did not hear Karmal's announcement on Radio Kabul during the day of the coup. Instead, they said, Radio Kabul maintained its normal broadcasting until 11 p.m. on Thursday. Then, they said, the station went off the air, after it came under military attack. Afterward, music was broadcast, they said.

Karmal's announcement, these sources said, was initially monitored on another radio frequency. The station, they said, incorrectly indentified itself as Radio Kabul. Only later, they said were Karmal's statements heard on Radio Kabul itself.

The State Department's charge that the Soviet Union prepared and broadcast Karmal's coup announcement was part of a pointed U.S. rebuttal to Soviet statements issued Sunday.

In an article in the Communist Party newspaper Pravda, the Soviet Union said that only a "limited military contingent" had been sent to Afghanistan to help repel what is described as internal subversion fomented partly by the United States. The Soviets denied any role in the Kabul coup.

Spokesman Carter attacked the Pravda account as being "replete with false, scurrilous and totally outrageous allegations."

He contended that the 30,000 to 40,000 Soviet troops estimated by State Department officials to have entered Afghanistan "are hardly a limited contingent." He argued that Soviet forces had already become "instrumental" in bringing about the coup before there were any reported requests by Afghanistan for Soviet help. He "categorically" rejected the Soviet allegation of U.S. and Chinese interfernece in Afghanistan.

"The U.S.S.R. decided to take matters into its own hands -- thus, the Soviet invasion," Carter said.

The Soviet move into Afghanistan also prompted criticism from two Republican presidential candidates. Former Texas governor John B. Connally and Sen. Bob Dole (Kan.) urged the Carter administration yesterday to withdraw the strategic arms limitation treaty (SALT II) from Senate consideration because of Soviet involvement in Afghanistan.

The Carter administraton has said it does not intend to withdraw SALT from the Senate because, it contends, the treaty is in the interest of U.S. security.

"We do not see SALT as some goody being given to the Soviet Union because they are good guys," State Department spokesman Carter said yesterday, echoing comments Sunday by national security affairs adviser Zbigniew Brzezinski.

Yesterday, President Carter discussed SALT II with Senate Majority Leader Robert C. Byrd (D-W.Va.). White House sources said later that the president remained unwilling to seek a delay of the Senate SALT debate. tOne senior official noted, however, that he now foresaw no possibility of an early Senate vote on the treaty.

State Department spokesman Carter also cited the Soviet move in Afghanistan as carrying potential significance for other Islamic nations.

"The true enemy of Moslem independece and of the Islamic region is not the United States or Washington," Carter said. "There are enemies -- and there are enemies," he added.

Nevertheless, he stopped short of saying Soviet involvement in Afghanistan would help persuade Iranian officials to release the U.S. hostages. Instead, the State Department spokesman argued, Iran and other Islamic countries should recognize that their "self-interest" does not lie with the Soviet Union. The implication was that if Iran acts in its self-interest, it will seek improved U.S. relations and free the hostages.