The South African ambassador angrily responded yesterday to the continuing protests outside his embassy in Washington, likening them to the 1979 takeover of the American Embassy in Iran. Meanwhile, two additional black leaders were arrested here and the protest movement mushroomed in cities around the country.

Ambassador Bernardus Fourie, in an interview televised on WJLA-TV (Channel 7), compared the protests to the embassy takeover in Iran, saying he was "rather surprised, shocked" that the United States -- "a country whose embassies have been violated" -- would allow "the sanctity of an embassy to be violated in this fashion."

Fourie's first public response to the protests came shortly after U.S. Rep. John Conyers Jr. of Detroit and William Simons, president of the Washington Teachers Union, were arrested outside the embassy at 3051 Massachusetts Ave. NW, in the second week of peaceful demonstrations against South Africa's racially segregating apartheid policy.

The arrest of Conyers, 55, an 11-term Democratic congressman who helped found the Congressional Black Caucus, and Simons, 60, brought to seven the number of prominent black leaders arrested here during the continuing protest, whose leaders are calling it part of a "Free South Africa Movement."

The movement's leaders have said they are seeking to win the release of black South African labor leaders who were jailed recently without any charges against them, and to pressure the Reagan administration to change its policy toward South Africa.

D.C. Del. Walter E. Fauntroy, who was arrested during a sit-in last Wednesday, said at yesterday's demonstration that the protest would continue and already is spreading across the nation.

Sympathetic groups already have formed in Boston and Los Angeles, where there have been demonstrations outside offices designated as South African consulates, according to a spokesman for TransAfrica, a foreign policy group that lobbies for African and Caribbean interests and is coordinating the protest movement. Spokesman David Scott said new groups also are forming in Chicago, Seattle and Houston.

Other prominent black leaders, including the Rev. Jesse Jackson and Coretta Scott King, likely will join in the protests later this week, according to TransAfrica's Scott.

Conyers and Simons were arrested on the misdemeanor charge of crossing police lines after a brief exchange with District police, as about 100 demonstrators chanted "Freedom, yes, apartheid, no" outside the embassy.

After police told Conyers and Simons they could not cross wooden barricades set 500 feet from the embassy, Conyers responded, "I feel duty bound to keep my agreement made with the brothers and sisters on the line, that we attempt to see the ambassador." With that, the two crossed the barricades and walked about 40 feet. Police then took them gently by the shoulders and arms, handcuffed them and took them away in a patrol car.

Simons was released and ordered to appear in D.C. Superior Court today. Conyers, following the example set by Fauntroy and others arrested previously in the protest, decided to spend the night in jail before his court appearance.

Yesterday, the Rev. Joseph Lowery, head of the Southern Christian Leadership Conference, and Rep. Charles Hayes (D-Ill.) pleaded not guilty in D.C. Superior Court to charges of unlawful entry, stemming from a similar protest Monday. Both were released on their own recognizance and are scheduled for trial Jan. 23.

Ambassador Fourie said the protests would not force change in the policies of his country, which he said "is striving to do as well as we can."

White House spokesmen could not be reached for comment, but a State Department official said, "We can understand the frustration many Americans feel over the slow pace of change in South Africa." Robert Bruce, director of public affairs for the Bureau of African Affairs, said that "demonstrations are part of the way of life" in America, adding that the U.S. would protect diplomatic missions here.

As to Fourie's remarks on the Iranian takeover, Bruce said, "I'll just let the South African ambassador comment on that."