The Reagan administration has alerted Congress to expect a proposal as early as next week for repeal of the five-year-old ban on covert or overt U.S. assistance to the rebel forces in Angola.

Presentation of such a proposal, which has been drawn up at the State Department for early transmission to Capitol Hill, would touch off a large controversy both here and abroad. It would be widely seen as the first step toward U.S. involvement in the Angolan insurgency, and as signaling a preference for military confrontation over political negotiations in dealing with the problem of Cuban forces in Africa.

A senior Department official told reporters that final decisions have not been made on legislative proposals to be sent to Congress along with revised foreign assistance totals made public yesterday. While that is literally true, according to informed sources the State Department is recommending that the prohibition on Angolan rebel aid be repealed, and officials expect that President Reagan will approve the move.

The ban on aid to Angolan insurgents was adopted in early 1976 under the sopnsorship of then-senator Dick Clark (D-Iowa) to half further CIA involvement in Angola by the Ford administration, after Cuban troops with Soviet aid turned the tide of battle in that country's civil war.

The Ford administration strongly resisted the Clark amendment, as it is known. The Carter administration at times favored lifting the ban, while also saying that it had not intention of resuming aid to Angolan rebels.

A measure repealing the Clark amendment passed the Senate last year under the sponsorship of Jesse Helms (R-N.C.), but died in a Senate-House conference because of the strong opposition of Rep. Stephen Solarz (D-N.Y.) and other House members.

Solarz said yesterday he will mount a vigorous fight against a Reagan administration effort to repeal the Clark amendment. Lifting the restriction on U.S. involvement in Angola, he said, "would be competely contrary to our larger interests in Africa" and would "fatally compromise" the chances of obtaining the withdrawl of Cuban forces from Angola through negotiated means.

The Angolan government, Solarz said, has made plain it is prepared to ask Cuban forces to return home if a political settlement can be obtained in neighboring Namibia, where South African forces and African nationalists have been battling. A U.S. decision to resume aid to rebel forces in Angola would, in Solarz' view, undercut the chances of a political settlement as well as generate very strong opposition to United States policy by most African states.

Reagan, in statements before he became president, strongly suggested that he favored U.S. support for UNITA, the Angolan guerrilla force headed by Jonas Savimbi, a chairsmatic leader once supported by the CIA. Savimbi was scheduled to visit Washington within a few weeks to make high-level contact with the new administration, but sources said yesterday that has been postponed.