The Senate, in an action certain to be controversial here and in Africa, voted last week to lift restrictions on the White House that effectively prevented any U.S. military aid or undercover help to rebels fighting the Marxist central government in Angola.

Though there is no evidence at this point that the Carter adminsitration plans to begin such aid or covert activities, the Senate action, if it becomes law, would allow the president to do so without making the action public and without an act of Congress specifically approving the aid.

The Senate action is a crucial first step in overturning a legal ban on such activities that was instituted four years ago in an amendment sponsored by then-senator Dick Clark (D-Iowa).

The Clark amendment was passed overwhelmingly by both houses of Congress in 1976, reflecting congressional fears in the immediate post-Vietnam era that the Ford Administration might involve the United States in the Angolan civil war.

Last Tuesday, in a voice vote that -- in sharp contrast to the 1976 events -- attracted little notice, the Senate approved an amendment to the fiscal 1981 Foreign Assistance Act. The amendment was first offered by Sen. Jesse Helms (R-N.C.) and would have repealed the Clark amendment entirely. However, a compromise measure in which Sen. Jacob K. Javits (R-N.Y.) and Sen. Paul Tsongas (D-Mass.) joined Helms as cosponsors was the one that passed.

Under the new amendment, if the president determined such aid was in U.S. national security interests, he could move ahead by privately informing the Senate Foreign Relations and House Foreign Affairs committees behind closed doors.

To become law, the new amendment would also have to be approved by the House. A conference committee meeting is scheduled for Wednesday, and several U.S. groups interested in African affairs are mobilizing to oppose the measure during these next legislative steps.

The new amendment is strongly opposed within the State Department's African Bureau and other quarters of the department as certain to raise immense political problems for the United States in Africa. This is so, officials said, because it comes at a time when relations between Angola and the United States seem to be improving and some progress also seems possible in negotiations over the independence of Namibia, talks in which Angola plays a key role.

In this view, the amendment is certain to be open to misinterpretation in Angola, since it seems to open the door to new covert or CIA-sponsored actions. U.S. officials, however say there is "absolutely no intention of mucking around in Angola."

The amendment also has produced some ambivalence within the Carter administration.

The Clark amendment was unique in that it was the only legal restriction of its kind that dealt with a single, specific country. The administration has generally resisted such measures on the grounds of opposing actions that restrict presidential authority.

There were incidents in 1978 when some officials specifically sought repeal of the Clark amendment. But President Carter said publicly afterward that the United States has no intention of getting involved in Angola, and officials claim that is still the policy.

State Department officials said privately the administration did not request the new amendment.

In making the case for the new amendment, Helms argues that the Clark amendment is no longer useful and is counterproductive because Soviet, Cuban, East German and even Nicaraguan troops are helping the Angolan regime, while the United States has its hands tied as far as helping opposing forces.

Helms said these countries "feel that they can continue to send troops into Angola with relative impunity . . . because the Clark amendment requires a full-blown congressional debate" that signals U.S. intentions to the Soviets and Angola and thus makes any military or covert aid useless.

Helms said the president must be given more flexibility.

Helms talked of a "new mood" emerging in this country, of a "spirit of reakwakening" to the dangers posed by the Soviets and their "surrogates." He cited the recent overwhelming vote in the Senate repealing the so-called Hughes-Ryan amendment, broader law restricting covert activities else where as another sign of turning away from what he called the earlier "overreactions" to the alleged abuses of covert action.