Castro's rise: fullest picture yet; Pushed to communism by America's misjudgment? Diary of the Cuban Revolution, by Carlos Franqui. New York: Viking Press, $25 hard-cover, $16.95 paperback. The Winds of December, by John Dorschner and Roberto Fabricio. New York: Coward , McCann & Geoghegan.$15.95.

So much is happening these days to Cuba that any enlightenment on how Fidel Castro launched it upon the slippery slope to communism and total dependence upon the Soviet Union -- and now, it seems, into economic and social disarray -- is of exceptional current interest and value.

The two works under consideration here have much to offer in this connection, although the main purpose of both is to tell the story of how Castro overwhelmed Fulgencio Batista and his well-equipped army and took over the country 21 years ago.

Unhappily, one has to conclude that the United States sped him on his way by muffing the chance that arose in 1958 and immediately thereafter of offering him wise and generous cooperation.

The trouble, as is made unmistakably clear in "The Winds of December," was that the State Department was at least as preoccupied with frustrating its resolute man in Havana, Ambassador Earl E. T. Smith, as in working out a viable policy toward the new Cuba. Smith believed single-mindedly that the sole alternative to Batista was communism. The State Department, on the other hand, imagined that Castro could be tamed by absorbing him into a basically pro-American junta.

Smith was, of course, closest to the m ark. This is particularly apparent when one reads that only a week before Batista fled, a State Department memorandum was telling President Eisenhower that the department believed the majority of Cubans shared its view in not wanting Castro to succeed to leadership of the Cuban government. Nothing could have been further from the truth, as anybody who saw the hysterical adulation with which Castro was welcomed to Havana in January 1959 would confirm.

Both books seem to show conclusively that while Castro was fighting in the Sierra Maestra he was not a communist. His own contradictory statements about this are valueless, as are so many of his political pronouncements, for the simple reason that he has usually said what suited or appealed to him at any given moment.

The Franqui diary (due in bookstores by mid-June) does make the telltale revelation that late in 1958 Raul Castro, Fidel's brother, "slyly and without a word introduced numerous communists into many sectors of the civil administration, into the rural committees, into the syndicates, and into other auxiliary voices of the second front." Was Raul then the villain?

The diary compiled by Franqui, who was for some years the official chronicler of the revolution, comprises over 500 pages of letters, notes, reports, and communiques written by almost everybody from Castro downwards while he and his tatterdemalions were plotting and then thrusting their haphazard and bloody path across Cuba from a swamp in Oriente to the Presidential Palace. It has sparkling and sometimes thrilling authenticity, especially in contributions by che Guevara, Frank Pais, and others, while the heat, dangers, and griefs of battle were agitating the writers' minds.

"The Winds of December" (published in April), produced by two editors at the Miami Herald, is utterly different. It is a minutely researched, ambitious attempt to get as close as possible to an eyewitness account of the last days of the revolution and the first days of the takeover. It is written in slick journalistic prose and resembles the literary equivalent of a projector flashing hundreds of slides briefly before the eyes. One quotation from Page 451 will suffice: "Politicians, military men, and rebels mingled happily on the red- and-gray, tile floor, their faces accented by the harsh light that came from bare lights dangling on cords from the 14-foot ceiling."

Two revealing themes course through the more somber Franqui volume. One is the ever-increasing tension, rivalry, and squabbling between Castro's own 26th of July Movement and the other radical bodies that joined it as, miraculously, it survived monumental blunders and disasters and went on to triumph. The other is the depressing one of defection, imprisonment, and worse that happened after that triumph to many who figure in the diary -- Che Guevara, Huber Matos, Manuel Ray, Camilo Cienfuegos, and others.

Castro's own writings in the Sierra make engrossing reading. All the facets of the personality we have come to know are exposed -- the cunning, the dazzling quality of leadership, and the ruthlessness, offset by emotional vacillation and childishness. And one choice revelation is that while in prison before he organized his revolution he was already comparing himself with Napoleon, and he wrote:

"I would honestly love to revolutionize this country from one end to the other. I would not be stopped by the hatred and ill will of a few thousand people, including some of my relatives, half the people I know, two-thirds of my fellow professionals, and four-fifths of my exschoolmates." Well, nor was he.