The Senate voted yesterday to end a ban on military aid to guerrillas fighting the Marxist government of Angola, raising anew the possibility of a shift in U.S. policy toward the mineral-rich southwest African country.

By a 63-to-34 vote, the Senate approved an amendment to the State Department authorization bill that would reverse a 1976 measure prohibiting military assistance to the pro-western National Union for the Total Independence of Angola (UNITA), led by Jonas Savimbi. The amendment was sponsored by Sen. Steve Symms (D-Idaho).

The Senate took similar action in 1981 only to have it die in conference with a House strongly opposed to new U.S. involvement in the now 10-year-old Angola struggle. It was not immediately clear whether the Symms resolution would meet a similar fate in the House.

State Department officials said the Reagan administration favored repeal of the so-called Clark amendment because the White House opposes all congressional measures that serve to restrict the president's hand in foreign policy. But they denied there was any plan to seek military or other aid for the anti-Marxist guerrillas in Angola.

The House, in a change of sentiment, has voted for open humanitarian, nonmilitary aid for anticommunist insurgents in Afghanistan and Cambodia, but the issue of Angola is more complex because congressional opinion is far more divided.

Symms, in Senate floor debate Monday, made no mention of proposing similar aid for UNITA, arguing only that repeal of the Clark amendment, named for former Democratic senator Dick Clark of Iowa, would encourage other African and Western European countries to provide assistance to the guerrilla movement.

Symms said the United States would be taking "the moral high ground" by providing UNITA with simply "a strong, unequivocal statement of political, moral and diplomatic support."

Sen. Claiborne Pell (D-R.I.), practically the only one to argue against the resolution, said repealing the Clark amendment "would lead the Angolan government and the international community to conclude that the United States intends to provide aid to UNITA."

He said it would increase Angola's dependence on the Soviet Union and Cuba and lead to more Cuban troops in the country.

An aide to Symms said after the vote that the senator had no immediate plans to raise the issue of U.S. humanitarian aid for UNITA, which gets substantial military and other backing from South Africa.

Nonetheless, the Senate vote is likely to raise again the issue of U.S. policy toward the Cuban-backed Angolan regime and whether Washington should resume aid to UNITA.

The United States, though it has no diplomatic relations with Angola, has been seeking its cooperation for a western and U.N. peace plan that would give independence to the South African-administered territory of Namibia and withdraw 25,000 to 30,000 Cuban troops from neighboring Angola.

After four years of on-again, off-again negotiations, however, U.S. talks with South Africa and Angola over the plan seem to have deadlocked. Meanwhile, a conservative Republican-led campaign in this country for a renewal of aid to UNITA has been gaining strength.

During the 1975-76 civil war at the time of Angola's independence, the Central Intelligence Agency secretly provided military aid to UNITA and another pro-western group in their joint bid to block the Marxist nationalist faction from seizing power. The bid failed and in early 1976 Congress cut off aid to the two pro-western movements.

Savimbi, with South African backing, continued his now 10-year-old guerrilla struggle against the government.