The Reagan administration asked Congress yesterday to repeal the ban on covert or overt U.s. aid to rebel forces in Angola, a move that is linely to generate major controversy in Washington and abroad.

Secretary of State Alexander M. Haig Jr., testifying before the Senate Foreign Relations Committee several hours before the administration's proposal was sent to Capitol Hill, described the issue as "a question of principle" involving "an unnecessay restriction" on the powers of the president.

He conceded, however, that there is "linkage" in the minds of Africans and others abroad between this proposal, the new administration's first controversial decision regarding Africa, and future administration policy in a series of major decisions still under review.

The ban on aid to rebel forces in Angola was adopted in 1976 at the high point of post-Vietnam sentiment that the United States should not become involved in another faraway civil war, and the expected congressional battle over its repeal is likely to rekindle those arguments. Several members of Congress have served notice they will fight repeal of the ban.

The intent and practical effect of the ban, sponsored by then-Sen. Dick Clark (D-Iowa), was to stop secret CIA support to Angolan factions fighting the Soviet- and Cuban-backed Angolan government. The State Department said yesterday that Regan administration officials are prepared to meet the leader of one of the formerly CIA-supported factions, Jonas Savimbi, who is expected here on a visit soon.

Another proposed change in U.S. law sent to Congress yesterday would repeal a prohibition on military assistance to Argentina. The ban was imposed in 1978 under the sponsorship of Sen. Edward M. Kennedy (D-Mass.) because of major violations of human rights, especially the large-scale torture and execution being practiced by security forces of the military government there.

Argentina's president-designate, Gen. Roberto Viola, completed a visit here this week in which he met with President Reagan, Haig and other high officials. Haig claimed yesterday that the situation in Argentina has "improved substantially" in recent months.

The proposals were sent to the Capitol as Haig toned down some of the rhetoric and shifted some of the positions taken Wednesday by himself and other senior State Department officials in congressional testimony.

Haig told the House Foreign Affairs Committee Wednesday of a "four-phased operation" or "hit list" for the communist takeover of Central America. "Phase One has been completed, the seizure of Nicaragua," he said, adding that this was to be followed, according to the plan, by communist takeovers in El Salvador, Honduras and Guatemala.

Yesterday Haig said that his earlier remarks "with respect to a broad strategic set of objectives" should not be taken as an assessment of the internal situation in Nicaragua. He said there are "a number of very important democratic elements seeking change" in that country, while the main levers of power are in the hands of "the extreme left."

Haig also expressed concern about intelligence reports that "sophisticated air defense weapons and possible tanks" are being shipped to Nicaragua from Eastern Europe.

The administration has not yet decided, he said, whether to resume economic assistance to Nicaragua. The aid has been suspended because of allegations that weapons and other support for the guerrilla forces in El Salvador have been transshipped through Nicaragua. Administration officials have said in recent days that the flow of arms appears to have slowed drastically or even stopped.

On another topic that made Thursday morning headlines, Haig told the senators that any talk of an administration plan to take action against Cuba is "pure speculation until the president has fulfilled his constitutional role" of making decisions.

He said no anti-Cuba recommendations have yet been sent to the White House by the State Department. "While we are considering the full rangle of options, and while we must consider all American assetts . . ., this in no way represents a final game plan," he said.

Haig made the statements in calming senatorial concern arising from testimony before the Foreign Relations Committee Wednesday by Undersecretary of State Walter J. Stoessel Jr. that specific plans, which "do not exclude anything," have been developed for dealing with Cuba if it continues to support the insurgency in El Salvador.

Following Stoessel's statements, Sen. Christopher J. Dodd (D-Conn.) asked for a confidential session of the committee to hear about the plans for striking against Cuba. Haig and Sen. Charles H. Percy (R-Ill.), the committee chairman, headed off this demand yesterday by insisting there are no plans to discuss.

On another decision in the making, Haig said he hopes and expects that Reagan will approve resumed U.S. aid to and alliance with Pakistan. U.S. aid was cut off during the Carter administration because of Pakistan's drive to produce nuclear weapons

Among the proposals sent to Congress yesterday was one to make it easier to aid Pakistan despite its continuing nuclear weapons program, by endorsing a waiver of non-proliferation laws to "promote the common defense and security" of the United States.

The chairmen of both the Senate and House subcommittees on Africa yesterday expressed concern about the timing of the administration's request for repeal of the ban on covert or overt assistance to Angolan rebels.

Sen. Nancy Kassebaum (R-Kan.) said that while she agrees that the ban should eventually be lifted, "we have to be cognizant of the signals it sends" in Africa. She also said an emotional debate on resuming U.S. covert action abroad could harm the domestic consensus necessary to advance Reagan's economic programs.

Rep. Howard E. Wolpe (D-Mich.) said he is planning subcommittee hearings March 31 and April 1 to focus on repeal, of the Angola ban. Wolpe said it would be "a very serious mistake of timing" to go forward with the repeal, which he said would be "read as a signal of intention to possibly subvert the Angolan government."