James Baldwin, whose passionate, intensely personal essays in the 1950's and 60's on racial discrimination in America made him an eloquent voice of the civil-rights movement, died of stomach cancer early yesterday at his home in St. Paul de Vence in southern France. He was 63 years old. At least in the early years of his career, Mr. Baldwin saw himself primarily as a novelist. But it is his essays that arguably constitute his most substantial contribution to literature. Mr. Baldwin published his three most important collections of essays -''Notes of a Native Son'' (1955), ''Nobody Knows My Name'' (1961) and ''The Fire Next Time'' (1963) - during the years when the civil-rights movement was exploding across the American South. Some critics later said his language was sometimes too elliptical, his indictments sometimes too sweeping. But then, Mr. Baldwin's prose, with its apocalyptic tone - a legacy of his early exposure to religious fundamentalism - and its passionate yet distanced sense of advocacy, seemed perfect for a period in which blacks in the South lived under continual threat of racial violence and in which civil-rights workers faced brutal beatings and even death. In the preface to his 1964 play, ''Blues for Mister Charlie,'' noting that the work had been inspired ''very distantly'' by the 1955 murder of a black youth, Emmett Till, in Mississippi, Mr. Baldwin wrote: ''What is ghastly and really almost hopeless in our racial situation now is that the crimes we have committed are so great and so unspeakable that the acceptance of this knowledge would lead, literally, to madness. The human being, then, in order to protect himself, closes his eyes, compulsively repeats his crimes, and enters a spiritual darkness which no one can describe.'' The novelist Ralph Ellison said yesterday, ''America has lost one of its most gifted writers'' and praised Mr. Baldwin as ''one of the most important American essayists, black or white.'' ''I would place him very high among writers,'' Benjamin DeMott, professor of English at Amherst College, said yesterday, ''in part because his work showed a powerful commitment to the right values and had a profound impact for good on our culture.'' Mr. Baldwin had moved to France in the late 1940's to escape what he felt was the stifling racial bigotry of America. Nonetheless, although France remained his permanent residence, Mr. Baldwin in later years described himself as a ''commuter'' rather than an expatriate. ''Only white Americans can consider themselves to be expatriates,'' he said. ''Once I found myself on the other side of the ocean, I could see where I came from very clearly, and I could see that I carried myself, which is my home, with me. You can never escape that. I am the grandson of a slave, and I am a writer. I must deal with both.'' Henry Louis Gates, professor of English and Afro-American Literature at Cornell University, said yesterday that Mr. Baldwin's death was ''a great loss not only for black people, but to the country as a whole, for which he served as a conscience.'' Mr. Gates said that Mr. Baldwin had ''educated an entire generation of Americans about the civil-rights struggle and the sensibility of Afro-Americans as we faced and conquered the final barriers in our long quest for civil rights.'' Despite the prominent role he played in the civil-rights movement in the early 1960's - not only in writing about race relations, but in organizing various protest actions - Mr. Baldwin always rejected the labels of ''leader'' or ''spokesman.'' Instead, he described himself as one whose mission was to ''bear witness to the truth.'' ''A spokesman assumes that he is speaking for others,'' he told Julius Lester, a faculty colleague at the University of Massachusetts at Amherst, in an interview in The New York Times Book Review in 1984. ''I never assumed that I could. What I tried to do, or to interpret and make clear, was that no society can smash the social contract and be exempt from the consequences, and the consequences are chaos for everybody in the society.'' This serene sense of independence was not simply a political stance, but an intrinsic part of Mr. Baldwin's personality. ''I was a maverick, a maverick in the sense that I depended on neither the white world nor the black world,'' he told Mr. Lester. ''That was the only way I could've played it. I would've been broken otherwise. I had to say, 'A curse on both your houses.' The fact that I went to Europe so early is probably what saved me. It gave me another touchstone - myself.'' Mr. Baldwin did not limit his ''bearing witness'' to racial matters. He opposed American military involvement in Vietnam as early as 1963, and in the early 1960's he began to criticize discrimination against homosexuals. Mr. Baldwin's literary achievements and his activism made him a world figure and to the end of his life brought him many honors in this country and abroad. The French Government made him a Commander of the Legion of Honor in 1986. Yet Mr. Baldwin was also clearly disappointed that, despite his undeniable powers as an essayist, his novels and plays drew decidely mixed reviews. ''Go Tell It on the Mountain,'' his first book and first novel, published in 1953, was widely praised. Partly autobiographical, since Mr. Baldwin himself was the son of a minister, the book tells of a poor boy growing up in Harlem in the 1930's under the tyranny of his father, an autocratic preacher who hated his son. Mr. Baldwin said in 1985 that in many ways the book remained the keystone of his career. '' 'Mountain' is the book I had to write if I was ever going to write anything else,'' he said. ''I had to deal with what hurt me most. I had to deal, above all, with my father. He was my model. I learned a lot from him. Nobody's ever frightened me since.'' But the reception accorded his other works was at best lukewarm, and his frank discussion of homosexuality in ''Giovanni's Room'' (1956) and ''Another Country'' (1962) drew criticism from within and outside the civil-rights movement. In a celebrated polemic in the late 1960's, Eldridge Cleaver, then a member of the Black Panther Party, asserted that the novel illustrated Mr. Baldwin's ''agonizing, total hatred of blacks.'' Another assessment of Mr. Baldwin was offered by the poet Langston Hughes, who observed, ''Few American writers handle words more effectively in the essay form than James Baldwin. To my way of thinking, he is much better at provoking thought in the essay than he is in arousing emotion in fiction.'' Mr. Baldwin's other works included the novel ''Tell Me How Long the Train's Been Gone,'' the stage plays ''Blues For Mister Charlie,'' and ''The Amen Corner,'' and ''The Evidence of Things Not Seen,'' a long essay on the murder of 28 black children in Atlanta in 1980 and 1981. Characteristically, Mr. Baldwin did not shrink from acknowledging the lesser view of his works of fiction, nor that his fame had slipped since the early 1970's. ''I'm very vulnerable to all of that,'' he said in a 1985 interview, referring to what he described in an early essay as the ''dangerous, unending and unpredictable battle'' of being a writer. ''The rise and fall of one's reputation,'' he mused. ''What can you do about it? I think that comes with the territory.'' ''Any real artist,'' he said, ''will never be judged in the time of his time; whatever judgment is delivered in the time of his time cannot be trusted.'' James Baldwin was born in 1924 in Harlem and attended DeWitt Clinton High School in the Bronx. He was a precocious writer, and by his early 20's was publishing reviews and essays in such publications as The New Leader, The Nation, Commentary and Partisan Review, and socializing with the circle of New York writers and intellectuals that included Randall Jarrell, Dwight Macdonald, Lionel Trilling, Delmore Schwartz, Irving Howe and William Barrett, among others. Yet, Mr. Baldwin was among the last one would have initially marked for a leadership role in a national movement. Soft-spoken, with a manner of speaking that mirrored his complex writing style, and physically slight, he thought of himself for many years as ugly, and wrote poignantly of his struggle to accept the way he looked. He is survived by his mother, Berdis Baldwin; five sisters, Paula Whaley, Gloria Smart and Barbara Jamison, all of New York City, Ruth Crum of Ossining, N.Y., and Elizabeth Dingle of Alexandria, Va., and three brothers, Wilmer, George and David, all of New York City. The funeral is to be held on Tuesday at noon at the Cathedral of St. John the Divine, 112th Street and Amsterdam Avenue. The idea of white supremacy rests simply on the fact that white men are the creators of civilization (thepresent civilization, which is the only one that matters; all previous civilizations are simply ''contributions''to our own) and are therefore civilization's guardians and defenders. Thus it was impossible forAmericans to accept the black man as one of themselves, for to do so was to jeopardize their status aswhite men. But not so to accept him was to deny his human reality, his human weight and complexity, andthe strain of denying the overwhelmingly undeniable forced Americans into rationalizations so fantasticthat they approached the pathological. - ''Notes of a Native Son'' (1955) People who shut their eyes to reality simply invite their own destruction, and anyone who insists onremaining in a state of innocence long after that innocence is dead turns himself into a monster. - ''Notesof a Native Son'' I am very much concerned that American Negroes achieve their freedom here in the United States. But Iam also concerned for their dignity, for the health of their souls, and must oppose any attempt thatNegroes may make to do to others what has been done to them. I think I know - we see it around usevery day - the spiritual wasteland to which that road leads. - ''The Fire Next Time'' If one is continually surviving the worst that life can bring, one eventually ceases to be controlled by a fearof what life can bring; whatever it brings must be borne. And at this level of experience one's bitternessbegins to be palatable, and hatred becomes too heavy a sack to carry. - ''The Fire Next Time'' Color is not a human or a personal reality; it is a political reality. - ''The Fire Next Time'' (1963) I do not wish to see Negroes become the equal of their murderers. I wish us to become equal toourselves. To become a people so free in themselves that they will have no need to - fear - others - andhave no need to murder others. - Spoken by the character Meridian Henry in the play ''Blues for MisterCharlie'' (1964) For our father - how shall I describe our father? - was a ruined Barbados peasant, exiled in a Harlemwhich he loathed, where he never saw the sun or the sky he remembered, where life took place neitherindoors nor without, and where there was no joy. By which I mean, no joy that he remembered. Had itbeen otherwise, had he been able to bring with him into the prison where he perished any of the joy hehad felt on that far-off island, then the air of the sea and the impulse to dancing would sometimes havetransfigured our dreadful rooms. Our lives might have been very different. But no, he brought with himfrom Barbados only black rum and a blacker pride, and magic incantations which neither healed norsaved. - ''Tell Me How Long the Train's Been Gone'' (1968)