Mayor Marion Barry will mark tomorrow's anniversary of Dr. Martin Luther King Jr.'s assassination by leading city employes in a District government-sanctioned antiapartheid rally and vigil at the South African Embassy.

The demonstration, which organizers say will be the largest gathering to date outside the embassy, is one of numerous apartheid protests scheduled in cities and on college campuses around the country this week to commemorate the civil rights leader, slain 17 years ago.

Barry, whose wife, Effi, has been among the more than 1,700 arrested at the embassy since weekday afternoon protests began there last November, has publicly endorsed the embassy demonstrations and plans to proclaim Thursday, April 4, as "D.C. Government Employees Day Against Apartheid."

The D.C. employes' protest will be held in addition to the usual late afternoon embassy demonstration and will take place from noon to 1:30 p.m. Participants are being encouraged to take the subway to Dupont Circle, and to assemble there for a sidewalk procession up Massachusetts Avenue to the embassy.

Joseph P. Yeldell, director of the D.C. Office of Emergency Preparedness who is organizing the city employes' rally and vigil with the mayor's blessing, said attendance is voluntary and that none of the planning for the event is being done on city time or at city expense. Employes taking part mustuse two hours of annual leave in addition to their lunch hour, he said.

Yeldell said officials working on the demonstration have met during their lunch hours and that 20,000 promotional flyers distributed in city agencies were printed privately. He said some local businesses are supporting the protest by chartering buses that will transport employes from central D.C. locations.

King was an outspoken critic of white-minority-ruled South Africa's policies of racial domination and urged an international economic boycott of that nation.

"In South Africa today, all opposition to white supremacy is condemned as communism, and in its name, due process is destroyed," King said in 1965. "A medieval segregation is organized with 20th century efficiency and drive; a sophisticated form of slavery is imposed by a minority upon a majority which is kept in grinding poverty; the dignity of human personality is defiled, and world opinion is arrogantly defied."

Organizers of what is being called a "National Protest Day for South African Divestment" say nothing has changed since King's comments 20 years ago. With Congress about to consider legislation that would impose economic sanctions on the Pretoria government, apartheid opponents are using the anniversary of King's death to step up their protest against U.S. ties and corporate investments in South Africa.

In addition to ongoing demonstrations at the embassy, similar protests are planned April 4 at more than a dozen colleges and universities that have funds invested directly or indirectly in South Africa and at the headquarters of several U.S. firms that operate there.

Joshua Nessen, staff member with the New York-based American Committee on Africa, which is coordinating the April 4 protest activities, said antiapartheid events will be held at Harvard University, where The Rev. Jesse Jackson will be the featured speaker; Princeton, with Rep. Ronald Dellums (D-Calif.); Berkeley, with Rosa Parks; Stanford, Columbia and 10 state universities.

Locally, students at George Washington University plan to hold a rally on campus and then stage a "funeral march" to the embassy. Students at American University, the University of Maryland, the University of the District of Columbia, Howard University and Georgetown University also are expected to join in the embassy protests.

Nessen said demonstrators also will hold protests against U.S. firms in 11 cities, including the Dearborn offices of General Motors; Mobil Oil headquarters in New York; and krugerrand gold coin dealers in St. Paul.

After 19 weeks of picketing and arrests outside the embassy, organizers of the Free South Africa Movement say they see the April 4 protests as a way of escalating the antiapartheid campaign at a time when Congress will decide what, if any, actions to take against South Africa.

"We want passage of legislation that finally puts the United States on the right side of an important human rights issue," said Randall Robinson, coordinator of the demonstrations.

Robinson calls the embassy protests, which have sparked similar activities in 22 other cities, "probably the longest-running sustained demonstrations in recent American history." He says they will continue indefinitely but that those who come to Washington to participate in them will now also be asked to help lobby for the antiapartheid legislation on Capitol Hill.

And, he says, the protesters will soon widen their campaign to include other visible symbols of South Africa.