More than 30 protesters were arrested outside the South African embassy here yesterday as organizers of the Free South Africa Movement employed a mass arrest tactic to publicize their demands for an end to white minority rule in South Africa.

On Wednesday, when nine protesters were arrested, organizers said the number of persons who will be arrested during the almost daily demonstrations at the embassy will increase each week as Congress begins to consider antiapartheid sanctions.

According to a D.C. police spokesman, organizers told police that the mass arrest approach on yesterday's scale will be employed only once a week. The Free South Africa Movement also uses the mass arrest tactic in New York, where as many as 22 people a day have been arrested in demonstrations outside the South African consulate on Park Avenue.

Previously, organizers in Washington used a "celebrity arrest" tactic in which politicians, religious and labor leaders, civil rights activists and other influential persons were arrested in groups of threes outside the Massachusetts Avenue embassy and charged with congregating within 500 feet of an embassy with intent to demonstrate.

Yesterday, police said, 31 demonstrators were arrested and also charged with violating the so called "500-foot rule," bringing to 113 the number of persons arrested since the demonstrations began here Nov. 21.

Rep. Mervyn M. Dymally (D-Calif.) was arrested outside the embassy but was not charged, D.C. police said, because he invoked his Congressional immunity.

Dymally, accompanied by two others, rang the doorbell of the embassy and asked to meet with the ambassador but was turned away for not having an appointment.

The congressman was then joined by a professor from the University of the District of Columbia, and they both gave lectures on "the lack of democracy in South Africa and the nature of democracy in America," according to Dymally, who was reached at his office last night after he was released by police.