President Carter is complaining that he has to operate under "very tight constraints" to counter with limited means the Soviet Union's unchecked ability "to send Cuban troops" into foreign adventures in Africa.

"And the Cubans respond without reticence," the president told a group of American editors on Friday in an interview made public yesterday.

The Carter comments contributed to a burgeoning and potentially explosive campaign by the administration to try to loosen the constraints on executive power imposed by a rebellious Congress as a result of the Vietnam war.

This looming clash is triggered by the conflict in Zaire. So far, that warfare has produced a French-Belgian-American airlift to rescue civilians caught in the conflict launched by a border-crossing force from Marxist Angola where there are an estimated 20,000 Cuban troops. Americans will avoid any involvement in the combat portion of that mission, U.S. officials have stressed.

But the Zaire fighting has forced to the surface simmering exasperation inside the White House over with Carter and Particularly national security adviser Zbigniew Brzezinski see as hamstringing limitations for checkmating Soviet-Cuban adventurism across the continent of Africa. On Tuesday, after a White House breakfast meeting with congressional leaders, House Minority Leader John J. Rhodes (R-Ariz.) reported Carter's "frustration at having his hands tied" for supporting "friendly nations."

Senate Democratic Leader Robert C. Byrd (D-W. Va.) strongly disagreed yesterday that Congress has "tied the president's hands" in any unwarranted measure - just as the State Department made public an eight-page listing entitled: "Restrictions on Presidential Authority To Provide Assistance to Foreign Nations and Conduct Foreign Operations."

At the top of the State Department summary is what is known to be the central target of the White House: legislation sponsored in December 1975 by Sen. Dick Clark (D-Iowa), chairman of the Senate Foreign Relations subcommittee on Africa. That legislation was introduced to cut off covert U.S. assistance to anti-Marxist factions then fighting in Angola, where Cuban troops supported by Soviet equipment made their first appearance in Africa.

The Clark amendment blocks any American aid, direct or indirect, for military or paramilitary operations in Angola without explicit congressional approval. Behind the scenes, the Carter administration is being urged by Saudi Arabia and other strongly anti-Marxist nations to help "pin down" the Cubans in Angola by supporting the guerrilla war still being conducted there by anti-Marxist nationalists.

Sen. Byrd said "I don't know why the question came up" about contraints on presidential power, although he said he discussed the matter with Secretary of State Cyrus R. Vance on Friday after hearing the first complaint at the White House meeting Tuesday.

"This State Department," Byrd said, "has been unable to provide documentation thus far that would indicate that the President's hands are tied in giving aid to friendly governments attempting to fight communist insurgency or incursions."

"I don't think," he said, "anyone should act under the misperception that Congress is timid, or that Congress will not act in the national security interest of the United States, if it is threathened." But Vietnam, Byrd said, illustrated "the unwisdom of getting deeply involved in a conflict thousands of miles from our own shores without our own U.S. security interests being involved."

Byrd agreed with Carter's decision to send Air Force transports to provide support for Belgian and French paratroops in Zaire, describing that presidential actions as "measured, deliberate and adequate."

Sen. George McGovern (D-S.D.), the 1972 presidential candidate and one of the champions of the Vietnam-born curbs on presidential power, expressed deep concern yesterday about what he sees in the offing on several fronts.

McGovern is especially alarmed that American preoccupation with Soviet-Cuban actions in Africa threatens to undermine completion of a new U.S.-Soviet nuclear arms control treaty.

Many fellow liberals, and conservstives, in Congress are saying that "the atmosphere is being poisoned for SALT," the strategic arms limitation talks. McGovern said in an interview that "I'm really pessimistic about SALT, with this anger building up."

McGovern said he is comparatively less alarmed that the administration will be able "to swing the pendulum all the way back on presidential power" to the pre-Vietnam war period.

"It may swing back a bit," McGovern said, "but it's not about to make an abrupt swing now." He said the executive branch "has just got to accept the fact that Congress is a partner in foreign policy - and a mjaor partner. They are just going to have to learn to live with it."

Carter, who repeatedly has warned against Soviet-Cuban military intervention in Africa's disputes, told visiting editors on Friday that:

". . . Congress placed very tight constraints on the president and any initiatives that can be taken, in the aftermath of the Vietnam war and the aborted effort to move into Angola, after they (the Angolans) got their independence from the Portuguese."

"I favor a lot of those constraints," Carter said. "The War Powers Act suits me fine where the president cannot initiate military action without consultation with the Congress. I think this is good.

"But within the bounds of the present law, which we are honoring rigidly," he said, "we are doing all we can" to see that Africa's problems are "resolved by leaders who live in Africa."

However, he said, "The Soviets and the Cubans are quite eager to provide military weapons to any group in a country where they might see a foothold there, an opening for them in the future for increased influence." And the Soviet Union, Carter added, is "very eager to send Cuban troops actually to be involved in the fighting."

In addition to the Angola-Zaire region, Carter said, "we are watching with great interest and concern now the degree of Soviet involvement in the internal matter in Ethiopia, concerning the Eritreans."

There are an American-estimated 15,000 to 17,000 Cuban troops in Ethiopia, and strategists are anxiously watching to see if they will be committed to the 16-year-old secessionist guerrilla war there in the province of Eritrea, bordering the Red Sea, opposite Saudi Arabia.

"We work with others who are interested in peace in Africa," Carter said, expressly noting that "the Saudi Arabians have been very helpful in providing some non-military aid when the countries get in bad economic circumstances." Carter made no reference to the fact that Saudi Arabian Foreign Minister Prince Saud Faisal was in Washington last week. Prince Saud was known to be urging the United States to join in sending sophisticated weapons and funds to anti-Marxist guerrillas in Angola and in Eritrea.

Carter said "we try to meet that (Soviet-Cuba) challenge on a non-military basis. We have a limited ability," he said, "to supply defensive weapons to those (friendly African) countries, under very tight constraint from laws that control my actions, and we take advantage of that."

At the same time, the Carter administration is trying to establish a foundation for shaking loose from some of the constraints.

That was one reason why administration spokesmen on Friday said that although they have no knowledge of Cubans fighting in Zaire, there is a Soviet-Cuban link to that conflict. It exists, the spokesmen said, because Cubans in Angola helped train the force that crossed into Zaire armed with Soviet weapons.

McGovern disclosed yesterday that last Tuesday he met for an hour and a half with the two senior Cuban diplomats in Washington. They strongly denied any Cuban complicity in the Zaire conflict the day before President Fidel Castro made a formal denial to the senior U.S. diplomat in Havana.

McGovern, who conferred with Castro in Cuba last year, said he met Tuesday with Ramon Sanchez-Parodi, head of the Cuban interest section in Washington, and his deputy, Teo Acosta, at their request.

They told him, McGovern said, "Let's concede that we have differences in Africa, but don't overlook the fact that we do want better relations with the United States despite what is happening elsewhere."

McGovern said, "They were making a plea for us not to foreclose other steps in our relations." They suggested, for example, he said, that it might be possible "to release" Cubans who claim dual citizenship, in the United States and Cuba, and who currently are denied permission to emigrate.

In addition to disclaiming any Cuban connection with the Zaire conflict, McGovern said, his Cuban visitors equally denied any intention by Castro to permit Cuban combat forces now in Ethiopia to enter the war in Eritrea - except on "one condition." That is, McGovern was told, if "a foreign government" entered that conflict - such as "the Sudan" or other nations.

According to a senior State Department official Friday night, there already are "several hundred" Cuban [TEXT OMITTED FROM SOURCE]