The day after President Reagan delivered his State of the Union address, the Black Leadership Forum, an umbrella group of 16 organizations, complained bitterly about theirinability to arrange a meeting with the chief executive.

"The greatest gap in 50 years has been allowed to develop between black leaders in America and the White House," lamented the group's spokesman, the Rev. Joseph P. Lowery of the Southern Christian Leadership Conference.

Lowery's reference to a half-century ago was timely: Franklin Delano Roosevelt, who had a striking collection of black leaders acting as his "Black Cabinet" and whose centennial is now being celebrated, became president nearly 50 years ago.

FDR wasn't the first American president to have black advisers, but he was the first to have so many--20. They became known as the "Kitchen Cabinet" because they sometimes met in the kitchen of their most famous member, educator Mary McLeod Bethune. Bethune had great access to Roosevelt through his wife, Eleanor. Bethune also had private meetings with FDR, who considered her charismatic and liked her style. "I am here to represent 14 million blacks," she would say in a commanding voice. "We are tired of crumbs and we are entitled to some slices of white meat."

Advisers like the "Black Cabinet," which is the subject of an exhibition at the Anacostia Neighborhood Museum, were not mere window dressing. They were partially responsible for several progressive executive orders signed by Roosevelt, including the Fair Employment Practices Act.

This group didn't accomplish as much T as it hoped, said one of its members, Alfred E. Smith, who still lives here in Northeast Washington. But, said Smith, "We wouldn't let it the effectiveness of the Black Cabinet fall flat."

In the years since, other black presidential advisers also have made a difference.

Bethune's White House entree continued during the Truman administration, which desegregated the armed forces after William H. Hastie resigned from the War Department because of racial discrimination. Truman later made Hastie the first black federal judge in the nation.

Republican Dwight D. Eisenhower named several blacks to government positions, but there was some concern among blacks nationwide when it was learned that the office that his closest adviser, Frederick Murrow, occupied was a remodeled broom closet.

Louis Martin, a vice chairman of the Democratic National Committee in the 1960s who was a confidant of Presidents John F. Kennedy and Lyndon B. Johnson, was one of the most effective, and soon earned the title, "godfather of black politics."

Martin had a large hand in bringing to Washington many blacks who later became prominent. Among them were Patricia Roberts Harris, who later joined the exclusive club of Americans who have held two Cabinet posts, former Army secretary Clifford L. Alexander, and Andrew J. Brimmer, the first black to serve on the Federal Reserve Board.

The cadre of blacks around Presidents T Richard M. Nixon and Gerald R. Ford included Stanley Scott, Robert Brown, Arthur Fletcher and attorney Samuel Jackson, and their primary inroad in those business-oriented administrations was the institution of black capitalism.

Jimmy Carter first turned to Martha M. (Bunny) Mitchell and later to Martin as key White House advisers on minority affairs. They were supplemented by Atlanta businessman Jesse Hill and Carter's longtime friend, Andrew Young, who for a time was U.S. ambassador to the United Nations.

That brings us to Ronald Reagan, who has avoided giving anybody the job of special assistant for minority affairs. The three blacks in top administrative positions--Melvin R. Bradley, Thad Garrett and HUD Secretary Samuel Pierce--have assumed the responsibilities informally.

It is probably no coincidence that Reagan's stock is so low in the black community. This president, who says he wants to be president of all the people, should take a lesson from history. In the absence of an official insider, a group like the Black Leadership Forum could make a difference.