THE PRICE OF THE TICKET; Collected Nonfiction, 1948-1985. By James Baldwin. St. Martin's/Marek. 690 pp. $29.95; THE EVIDENCE OF THINGS NOT SEEN. By James Baldwin. Holt, Rinehart & Winston. 125 pp. $11.95.

WHEN JAMES BALDWIN was a high-school student in Harlem, he had a brief conversation with his father that he later recalled as "the one time in all our life together when we had really spoken to each other." His father was a preacher, a stern and forbidding man who had encouraged his son's own apprenticeship in the pulpit but now sensed that the prodigy was becoming prodigal. "You'd rather write than preach, wouldn't you?" his father asked, to which the astonished youth replied honestly, "Yes."

This encounter, which Baldwin reports in his brilliant essay "Notes of a Native Son," is significant not merely because it marks the moment when he committed himself to the writing that eventually made him famous, but because it reminds us that he has always been as much preacher as writer. He forsook the church long ago and ever since has been a skeptic so far as matters ecclesiastical are concerned, but his upbringing in a pious household and his training as boy revivalist left marks that no amount of apostasy could erase. His prose has the rhythm, the rolling and irresistible cadences, of hellfire and brimstone; his expository method is that of the homily, a mixture of logic and passion that is both rational and emotive.

The subject of his sermons is almost always the life that black Americans live, but his real audience -- his congregation, if you will -- is white America. This is not to say that he has an insubstantial black readership -- to the contrary, his following among black Americans is large and deservedly loyal -- but that he has chosen to be the messenger of the downtrodden, and that in this role his words are directed principally to those whom he perceives as their oppressors. Depending on his mood and the aims he hopes to accomplish, these words can be angry, cajoling, contemptuous, witty, sarcastic, apocalyptic, compassionate; but they are always urgent, always intended to force the reader into a heightened awareness of the black situation and its potential ramifications for all America.

The more than four dozen essays collected in The Price of the Ticket display Baldwin in all his guises. They also, though quite unwittingly, provide painful evidence that since his great success in 1963 with The Fire Next Time -- originally published the previous year in The New Yorker as "Letter From a Region in My Mind" -- Baldwin's skills have steadily deteriorated; this conclusion is most unhappily confirmed by The Evidence of Things Not Seen, an excruciatingly slipshod meditation on the Atlanta child murders. What has happened to Baldwin quite simply is that since he moved to a prominent position on the public stage, the preacher has taken over from the writer; for two decades his rhetoric has grown steadily more bombastic, grandiloquent and predictable, while the humor, sensitivity and self-mockery of the early essays have virtually disappeared.

SO MUCH HAS been written about Baldwin's work that it seems rather pointless to provide further exegesis of it here. Suffice it to say that reading his essays from the 1950s and early '60s for the first time in many years, I was struck as forcibly as ever not merely by their power and passion, which can be quite overwhelming, but also by their civility and restraint. The Baldwin of those years -- the Baldwin whose essays were collected in Notes of a Native Son and Nobody Knows My Name -- was a startling voice from a land called black America that white America scarcely knew, but he was a voice that sought to reason with us even as he exposed our hypocrisies and cruelties. He was angry, with ample reason, but he appealed to the decent and humane in us; he tried to make us understand that we were all in this business together, and that a genuinely egalitarian society served the self-interest of white America as well as black.

In the best of these essays -- "Many Thousands Gone," "The Harlem Ghetto," "Fifth Avenue, Uptown," the title pieces of the two aforementioned collections -- Baldwin wanted to submerge us in the squalor and despair of the ghetto, but he also wanted to interest us in the people who lived there and to make us realize that they were just like us, only with different skin color. He spared us almost nothing -- the fury of "Letter From a Region in My Mind" is breathtaking -- yet he reached out to us. Toward the end of Notes of a Native Son, contemplating the death of his father, he wrote:

"This was his legacy: nothing is ever escaped. That bleakly memorable morning I hated the unbelievable streetthe Negroes and whites who had, equally, made them that way. But I knew that it was folly, as my father would have said, this bitterness was folly. It was necessary to hold on to the things that mattered; blackness and whiteness did not matter; to believe that they did was to acquiesce in one's own destruction. Hatred, which could destroy so much, never failed to destroy the man who hated and this was an immutable law."

Unfortunately, though, it is a law whose effects Baldwin himself seems to have felt. When in the '60s he became one of the most prominent "spokesmen" for black America, he seems to have felt it necessary to move with the crowd rather than maintain the distance he had theretofore kept from it -- and the crowd was moving in the very directions Baldwin himself had deplored. During the '60s and '70s he came into contact not merely with Martin Luther King Jr., whom he revered, but also with Muslims and Panthers, whose more racist and apocalyptic messages he absorbed into his own. More and more frequently he issued insupportable blanket condemnations of whites: "Blacks are often confronted, in American life, with such devastating examples of the white descent from dignity; devastating not only because of the enormity of the white pretensions, but because this swift and graceless descent would seem to indicate that white people have no principles whatever."

THAT WAS published in 1976, in a pointless and discursive piece -- a short book, actually -- called The Devil Finds Work. Now, in his introduction to The Price of the Ticket, Baldwin goes further. "There was not, then," he writes, "nor is there, now, a single American institution which is not a racist institution." In three decades have we made any progress toward a more egalitarian society? Of course we have. But Baldwin writes: "Spare me, for Christ's and His Father's sake, any further examples of American white progress. When one examines the use of this word in this most particular context, it translates as meaning that those people who have opted for being white congratulate themselves on their generous ability to return to the slave that freedom which they never had any right to endanger, much less take away."

Not merely is this twaddle, it is badly written twaddle: gassy, inflated, seat-of-the-pants rhetoric that has far less to say than its orotund phraseology at first leads one to believe. The same is true, though even more so, of the prose in The Evidence of Things Not Seen. This slender book, which was written on commission for Playboy, is a piece of nonsense in the literal meaning of the word: it makes no sense at all. It is a tortured effort to squeeze out the required number of words, an effort that leads Baldwin into wild, and wildly irrelevant, speculations on everything from emasculation to "the European horror," which is to say white culture. The book is riddled with exclamation points and italics, names are dropped in every direction -- as, alas, they also are in the later essays in The Price of the Ticket -- and self-congratulation is everywhere.

For a writer of Baldwin's gifts, The Evidence of Things Not Seen is a pathetic embarrassment; certainly it is embarrassing to read. That he should have gone into so great a decline is a mystery, though the burdens and distractions of fame may well have had something to do with it. Whatever the case, the writer who gave us Notes of a Native Son is nowhere to be found in The Evidence of Things Not Seen; and if the writer who once warned us against hatred has not transformed himself into a racist, he is certainly putting on a good imitation of one.