The House Banking Committee voted yesterday to prohibit the Export-Import Bank from supporting any U.S. exports to South Africa unless that country makes progress toward ending its system of racial segregation.

If the committee's action is approved by the full Congress, it would further reduce South Africa's ability to purchase goods from the United States.

Despite already existing restrictions, the Export-Import Bank is an important source of funding for trade between the two countries. It has approximately $200 million invested in various programs to support South African purchases of U.S. goods.

The committee's action came as it approved a bill raising lending authority from $25 billion to $40 billion at the bank, a government agency whose purpose is to boost U.S. trade by providing financing for overseas sales.

The South Africa amendment was offered by Rep. Paul E. Tsongas (D-Mass.). The committee, after rejecting several attempts to eliminate or water down the Tsongas amendment, adopted it in a form stating that the Export-Import Bank cannot support any South African business transactions unless and until the president determines that progress has been made toward eliminating South Africa's apartheid system.

Since 1964, the bank has been prohibited by regulation from making direct loans to South African purchasers of U.S. exports. However, it has continued to provide various forms of insurance and other guarantees for loans from private U.S. banks.

In the Senate Banking Committee, which also has the Export-Import Bank authorization under consideration, a pending amendment by Donald W. Riegle (D-Mich.) is almost identical to the Tsongas amendment.

In another action yesterday, the House committee approved an amendment offered by Les AuCoin (D-Ore.) that would exempt China from restrictions on Export-Import Bank loans to communist countries.

Under existing law, the bank cannot make such loans unless the president grants an exemption on grounds that they are in the national interest. Such presidential exemptions have been made for Poland, Romania and Yugoslavia.

AuCoin offered his proposal to relieve China of this requirement to encourage improved commercial ties.However, it is largely symbolic, since the Chinese have not sought any bank credits from the United States.

The Banking Committee's South Africa vote opened a week that is expected to see close congressional attention to the question of U.S. assistance to countries accused of violating the human rights of their citizens.

Most of the activity will take place in the House International Relations Committee, which is scheduled to consider parts of the Carter administration's fiscal 1979 requests for military aid to allies.

Rights advocates in and out of Congress have criticized some of the requests on grounds that they counter the administration's stated human-rights policy by helping repressive regimes.

Last week the International Relations Committee cut $5 million from the administration's military request for the Philippines, on human rights grounds.

Because of current negotiations for the right to keep air bases in the Philippines, the administration had asked Congress to continue military aid to President Fernando Marcos's government at fiscal 1978 levels.

That involved a request of $18.1 million for grants of military equipment, $18.5 million to finance purchases of additional U.S. equipment, and slightly under $1 million for military training.

However, the committee cut the grants request to $13.1 million, to protest allegations of torture and imprisonment of Marcos opponents and of widespread fraud in recent elections.

On another human-rights front, congressional sources said Sen. Edward M. Kennedy (D-Mass.) is expected to make a major speech this week criticizing the administration for allegedly easing restrictions on aid to the military dictatorship in Chile.

The sources said a major target of Kennedy's criticism will be a loan, announced by the Agriculture Department April 24, of $38 million to Chile by the Commodity Credit Corp. to finance purchases of U.S. wheat and of beef cattle for breeding.

The CCC provides financing to other countries at slightly less than commercial rates to boost the sale of U.S. farm products.

In justifying the loan, administration officials said its primary purpose was to aid American farmers. In addition, they said they believe the human rights situation within Chile is improving and approved the loan to encourage further easing of repression.