The Food and Drug Administration said yesterday it plans to begin testing at 2,100 food additives on the market to assure their safety. A consumer activist immediately condemned the program as a means of buying time while consumers remain exposed to dangerous chemicals.

Acting FDA Commissioner Sherwin Gardner announced the new tests in testimony at a Senate subcommittee headed by Gaylord Nelson (D-Wis.). Nelson has criticized the FDA for allowing some chemical food additives to remain on the market after scientists have linked them to cancer and other diseases.

Nelson said the average American eats five pounds of food additives a year. Nelson said there are more kinds of food additives approved for use in the United States than in any other nation. The amount of additives has more than doubled in recent years to a total of more than 1 billion pounds annually, he said.

Gardner said all preservatives, colors, flavors and substances that may get into food from packaging will undergo scientific re-evaluation beginning in March. "Science is dynamic and a food additive judged safe by the science of 1970 may very well be suspect by the science of 1977," he said.

He said that profiles on each of the food additives will be established within 18 months and FDA may then restrict use of some additives or remove them from the market.

However, the next witness, Dr. Sidney Wolfe, director of Ralph Nader's Health Research Group, attacked the FDA-action.

He accused the FDA of "protecting the food industry, instead of protecting the public" and said chemicals should be taken off the market as soon as there is scientific doubt about their safety.

Gardner disagreed with this position in his testimony. He said ordering a product off the market because of a health scare that eventually proves to have been false "would ultimately mean less, not more, protection for the American consumer."