Because Charles S. Murphy was self-effacing in a town of self-promoters, genuinely modest in a city of the proud and arrogant, few beyond his circle of intimate friends knew of the great range and quality of the service he rendered in nearly half a century of life in Washington. And so, when he died on Sunday at the age of 74, even The Post carried only a routine obituary notice in the next day's paper.

One reason for the neglect, I suppose, is that Charlie Murphy's stature and influence peaked more than 30 years ago, during the late years of the Truman administration, when he was the pivot on which the White House turned. Murphy was not one of the president's bourbon-drinking and poker- playing cronies; he was, rather, the man on whom Truman leaned intellectually to keep the program of his administration consistent, liberal and honest. This Murphy did by controlling the flow of words from the presidential office--messages to Congress, speeches, policy-setting communications of all kinds, everything but the letters the president personally took to the corner mail box to keep them out of Murphy's hands. By being in charge of the words that explained the president's program, Murphy became perforce the coordinator of program development as well.

But few outside the White House and the top levels of government knew the scope of his responsibilities even then. Men who had held the comparable post before, like Sam Rosenman for Roosevelt, and the men who did so afterward--Ted Sorensen, Joe Califano, Stuart Eizenstat and the Meese-Deaver- Baker combination today--were well-known to the world at large. But Charlie Murphy was the last --perhaps the first as well--truly anonymous White House aide. The one thing that could upset this normally unflappable man was to see his name in the papers. He saw to it that that rarely happened.

Murphy would have been the last to say that he exercised power. He might accept the word "influence," but I doubt his concept of his role would admit even that. Yet he exercised both, as the man the president held in closest trust. Their partnership was rooted in a common origin: both had grown up in the rural south, both had had to unlearn the white-black relations they had known as boys, both suffered hardship in the Great Depression. And both were men of simple and strong convictions that happened to coincide.

Indeed, Charlie Murphy, like Truman himself, could be called a man of certitudes. There were some things that he knew beyond any doubting, and those certitudes were echoed in the Truman speeches that--it can be said now--Murphy either wrote or was in charge of writing. Murphy, like Truman, just knew that Republicans were bad for the country, and he made no effort to conceal his intense partisanship. He knew that government could be a powerful instrument for improving the lot of common folks. He knew that blacks had to be granted their full measure of civil rights. So his influence--or power--was on the side of New Deal liberalism in its purest form, and the development of Truman's Fair Deal as a worthy successor to FDR's reforms. And, above all, he knew that Harry Truman would go down in history as one of the greatest of American presidents.

His post-White House years were devoted to expressing those convictions in whatever opportunity arose. He wrote speeches for Lyndon Johnson's vice presidential campaign lambasting the Republicans in Truman's own inimitable style. As a trustee of Duke University, he was a leader of the protest movement that blocked the erection of Richard Nixon's library on campus. He was the prime mover in organizing the National Democratic Club. As undersecretary of agriculture, he labored to right the wrongs that he felt had been visited, since time immemorial, on small farmers--especially the black farmers of the South. And he devoted enormous amounts of energy to the Truman library at Independence as a means of sustaining and, whenever possible, embellishing the Truman image.

One final anecdote: President Truman was on a political speaking tour that would take him into North Dakota. That state, by coincidence, had just suffered a major flood. The appropriate government agency had concluded that the losses warranted much of North Dakota's being declared a disaster area eligible for federal assistance. How timely, suggested an assistant speech writer, for the president to announce while in the state that he was declaring it eligible for aid.

But from Charlie Murphy came a flat rejection: the president would never play politics with federal disaster programs. The announcement would be made by the proper agency and only after the president had left the state. How many advisers to presidents, in these later days of public-relations presidencies, would have made that decision?