President Carter today defended his policies of noninvolvement in the Sino-Vietnamese border war and the revolution in Iran, but said the United States would take action if its "vital interests" are threatened.

Receiving an honorary engineering degree from Georgia Tech in a day of homecoming to his native state, Carter also argued the case for a new strategic arms limitation treaty (SALT), and insisted such a pact should not be linked to regional confrontations involving the Soviet Union.

The main line of the address, which was interrupted a dozen times by applause, was defense of his foreign policies against critics who have charged them with weakness and irresolution.

Carter said he does not oppose change, despite its turbulent darker side, and that "the United States cannot control events within other nations. A few years ago we tried this and we failed."

As a way of reassuring allies, Carter said additional military assistance is being considered for Indian Ocean nations threatened by spreading instability. White House officials said a request for a supplemental appropriation to aid Thailand, Pakistan and perhaps other nations is being discussed with members of Congress.

The address at Georgia Tech, where Carter was a student for a year in 1942-3 before starting at the U.S. Naval Academy, was his first statement on the growing dangers in east Asia since the Chinese invasion of Vietnam last weekend.

Carter referred to the Chinese action as a "frontier penetration," and said it had taken place as a result of the Vietnamese "invasion of Cambodia. He said the United States will continue trying through the United Nations and direct diplomatic appeals to convince China to withdraw from Vietnam, and Vietnam to withdraw from Cambodia.

"We will not get involved in conflict between Asian communist nations," he said to loud applause. "Our national interests are not directly threatened, although we are concerned at the wider implications."

At the same time, he expressed deep concern that the conflict could widen further "with unforeseen and grave consequences for nations in the region and beyond". He added, "In any event, we are fully prepared to protect our vital interests wherever they may be challenged."

Senior U.S. officials traveling with the president declined to spell out how expansion of the conflict might involve U.S. vital interests or what Carter's action then might be. The officials said U.S. reports from the battle area did not give a clear picture of what the Chinese are doing but they expressed doubt that China is pulling back its force at present.

One official said that some Soviet response to the Chinese action is anticipated. There were suggestions that some quarters in the administration believe possible Soviet action to establish a naval base at Camranh Bay in Vietnam might involve U.S. interests in a direct way.

Turning to Iran, Carter described the revolutionary situation there as the product of internal social political, religious and economic factors.

"Those who argue that the United States should or could intervene directly to thwart these events are wrong about the realities of Iran... We have not and will not intervene in Iran, yet the future of Iran continues to be of deep concern to us and our friends and allies," he said.

In what White House officials said was a reference to Soviet broadcasts, he said it was also wrong to "spout propaganda that protecting our own citizens is tantamount to direct intervention."

Without naming the Soviet Union, Carter called on other nations not to become involved in the Iranian revolution. "If others intervene, directly or indirectly, they are on notice that this will have serious consequences and will affect our broader relationship with them," he said.

Such consequences evidently would not include major impact on the final stage of SALT II negotiations. Carter went out of his way to say that "I will seek both to conclude a SALT II agreement and to respond to any Soviet behavior which adversely affects our interests."

To reject SALT, he argued, would make the competition in strategic armaments "even more dangerous" and bring "an added dimension of danger" to each confrontation or point of friction in regional disputes.

A senior official who briefed reporters on a background basis aboard Air Force One was more explicit: "In effect, there is no linkage between positive or negative behavior. We want SALT whether our relations are good or whether our relations are bad. We want SALT whether we are cooperating. We want SALT whether we are competing."

[In Washington, administration sources reported that efforts to complete a new SALT pact with he Soviets have run into a Soviet stall, at least temporarily.]

[Last Tuesday, Secretary of State Cyrus R. Vance made proposals to Soviet Ambassador Antatoliy F. Dobrynin for settling the last three unresolved substantive issues. Dobrynin returned to Vance's office Monday, and administration officials expected him to bring a reply. But he had "no new instructions," according to an authoritative source, so the negotiations remain stalled.]

Asked how Soviet behavior could affect broad relations with the United States, the official said, "the whole fabric" and the "tone" of the relationship could be affected if U.S. vital interests are challenged.

Carter said agreement with the Soviets has been reached on "most of the major components" of what he called "the emerging SALT II treaty." He described in general terms the limitations on Soviet action called for by the treaty terms, but said the pact "will also permit us and our allies to pursue all the defense programs we believe we may eventually need."

He mentioned, as possibly needed and permitted under SALT II: the MX land-based missile; the Trident submarine and missile; air-, ground-and sea-launched cruise missiles; a cruise missile aircraft carrier, and a new penetrating bomber.

The Georgia Tech address had been planned as a major statement on the strategic arms treaty. The topic was shifted to cover regional problems more extensively late last week as Americans were evacuated from Iran in large numbers and China invaded Vietnam. One official said part of the reasoning was a reluctance to emphasize U.S.-Soviet accord at a time when Moscow might be preparing to intervene against China.

Carter said the United States seeks to provide "the bedrock of global security and economic advance in a world of unprecedented change and conflict."

He said the nation's "four fundamental security responsibilities" are "to provide for our nation's strength and safety; to stand by our allies and friends; to support national independence and integrity; to work diligently for peace."

Carter arrived in Atlanta wearing pancake makeup to cover facial bruises suffered in a skiing spill at Camp David Sunday night. White House officials said the bruises, described as very noticeable before the makeup was applied, came about when Carter caught a ski under a crust of ice and landed on his face.