Arrests outside the South African Embassy resumed yesterday after a holiday break, and leaders of the Free South Africa Movement said the number of people going to jail will increase week by week as Congress begins considering proposed antiapartheid sanctions.

Nine persons were arrested yesterday for demonstrating in front of the embassy on Massachusetts Avenue NW, where the protest has entered its seventh week. So far, according to its organizers, 427 people have been arrested in 11 cities since the protests against apartheid were launched at the embassy here Nov. 21.

"We're going to keep this movement alive and growing across the country," said Randall Robinson, cochairman of the Free South Africa Movement. He said demonstrations should spread to 20 cities by next week and that the number of arrests will rise in an effort to gain congressional support for sanctions against the South African government and its policies of racial separation.

"Between now and February, the numbers will be much larger," said Robinson, who called yesterday's arrests "one of the smaller numbers" of those being planned.

As about 50 supporters watched and cheered, the nine "witnesses" slated for arrest were driven to the front of the embassy in an orange church van. Following the usual pattern of the protests, the nine went to the embassy's front door and asked to speak to the ambassador. After this request was denied, they began singing a civil rights anthem and were arrested by police and charged with a misdemeanor violation of demonstrating within 500 feet of an embassy.

Organizers of the protest are trying to win freedom for imprisoned black leaders in South Africa and to force the Pretoria government to hold discussions on sharing power with the majority black population.

Arrested yesterday were Marcus Raskin, David Cortright and Joseph Miller of the Committee for a Sane Nuclear Policy; Nancy Randolph and Norma Taylor of the Council on Social Workers Education; Peter Stahmen, a University of Florida professor; Bobbi Blok, a member of the D.C. State Democratic Committee; Brent Dillingham of the Indian Law Research Center; and John Steinbach of the Gray Panthers.