Blacks for Reagan: Three days after about 300,000 blacks gathered at the Lincoln Memorial last Saturday for the 20th anniversary of the civil rights march on Washington and produced an abundance of anti-Reagan rhetoric, another group of politically-minded blacks gathered at the same spot to pronounce a different message.

Three black speakers announced the formation of "Blacks for Reagan", which will conduct an "information campaign" to convince black Americans that reelecting President Reagan would be a smart move for them in 1984.

They are Mabel King, a Los Angeles actress, Henry Miller, a Los Angeles builder, and Jay Parker, president of the Lincoln Institute, a D.C.-based think tank, and a public relations representative of Venda, one of four states set up by South Africa as a homeland for blacks. Miller said that opportunity is the best cure for poverty because "Negroes . . . ask nothing more of their government than to be allowed the greatest possible freedom to develop their own destinies. Our best chance at this lies with President Reagan."

Parker said the group will spend $200,000, which will be provided by the National Conservative Action Committee, mostly on advertising with black-owned newspaper and television and radio stations. Despite the bankroll, Parker was not terribly optimistic about the group's prospects. He said he expects at best to hold onto the 10 percent of the black vote for Republicans in 1980. "Maybe we'll go higher some day, but not next year," Parker said.

The 300,000 who marked the 20th anniversary of the civil rights march on Washington included blacks and whites, not just blacks, as reported incorrectly yesterday. CAPTION: Picture, Parker, flanked by Miller and King, says the "Blacks for Reagan" plans to spend $200,000 to reelect the president. UPI