For the first time since antiapartheid protests began at the South African Embassy a year ago, there were no arrests there yesterday, although the weekday afternoon demonstration was held as usual.

Randall Robinson, national coordinator of antiapartheid protests organized by the Free South Africa Movement, said the yearlong string of arrests was broken because the group had a last-minute cancellation.

He declined to say who or how many people had volunteered for arrest.

Yesterday was the first anniversary of the embassy protests, which began last Nov. 21 on Thanksgiving Eve, when Robinson and two others were arrested inside the embassy.

Since then, more than 4,000 persons, including about 2,900 embassy demonstrators, have been arrested in antiapartheid protests around the country. Organizers plan officially to mark the protest's anniversary Wednesday, Thanksgiving Eve, with a march to the embassy and more arrests.

At their height, embassy arrests numbered more than 100 a day, and numerous civic, church and labor groups as well as private citizens were volunteering to be arrested as a protest against South Africa's racial policies. Most were charged with demonstrating within 500 feet of the embassy, a misdemeanor.

In recent weeks, however, there have been as few as one arrest a day.

Robinson said yesterday that embassy demonstrations will continue but may be scaled back as the antiapartheid campaign is extended to include corporations with business ties to South Africa.