MacKinlay Kantor, 73, one of America's best known and most prolific authors, died yesterday in Sarasota, Fla., of heart disease.

In 1955, Mr. Kantor published "Andersonville," a novel about the horrors of a notorious Confederate prison camp in the Civil War. The book, which Mr. Kantor referred to as "Big A," brought instant critical acclaim and the Pulitzer Prize in the year following its appearance.

In 1975, just in time for the nation's Bicentennial, he published "Valley Forge," a novel about the awful winter spent in that Pennsylvania area by George Washington's army in the Revolutionary War.

For "Valley Forge," Mr. Kantor received an award from the Freedoms Foundation. However, one critic said that the book was so bad that reading it was as much of an "ordeal" as the winter it described must have been.

But taken with "Andersonville" and "Long Remember," a 1934 novel about the Battle of Gettysburg, "Valley Forge" serves to illustrate Mr. Kantor's long fascination with the wars of the United States.

Those three books in no way illustrate the scope and range of Mr. Kantor's writings. He wrote children's books and movie scripts. He was a war correspondent in World War II and in the Korean conflict. He wrote hundreds of short tories and articles.

In 1972, he wrote "Irene, I Love You," a book about his life with Irend Layne, whom he married in 1926, and who was with him when he died.

"Glory for Me," a novel in verse published in 1945, was the basis for the Oscar-winning film classic, "The Best Years of Our Lives." "God and My Country," published in 1954, was the basis for the Walt Disney film, "Follow Me, Boys!"

In 1956, Mr. Kantor criticized officials in Sarasota, where he had established his residence in 1936, for their refusal to set aside a beach on the Gulf of Mexico for the use of blacks in the then-segregated South.

"My stories have appeared in an appalling number of magazines, sublime, ridiculous and penny-dreadful," Mr. Kantor once said. "I used to write a great deal of stuff for the pulp detective-and-crime story magazines, in the years when I had to make my living that way, and I don't think that my rather complicated talents were harmed in the least. The severe routine of such endeavor stimulated my sense of plot and construction, which needed such stimulation very badly indeed."

However he developed as a writer, Mr. Kantor first tasted critical and financial success with "Long Remember," his first major effort at a historical novel.

He reached the height of his skills in this genre with "Andersonville." The book recounts the atrocious conditions that were allowed to prevail in the Confederate prison cammp at Anderson Station, Ga., where thousands of Union soldiers were permitted to die in conditions that have invited comparison with the Nazi concentration camps of World War II.

If "Gone With the Wind," the great popular novel by Margaret Mitchell, portrayed the Old South as a land of cultured people and genteel ways, "Andersonville" stripped the Civil War of its romanticism. The power of the novel lies in the author's use of one chilling detail after another to describe life and death in the camp.

The scope of "Andersonville" is wider than the camp itself. Through various characters, it becomes a panorama of the war as a whole and of life in America in the 1860s.

Mr. Kantor attempted to use the same technique with "Valley Forge." It is distinctly less successful. At one point, Mr. Kantor has George Washingtton wonderin "in impish curiosity" whether the United States will "Put my picture on their money!"

This was written by the same man who toel reporters in 1957 that the problem with most historical novels was that they were inaccurate.

"We opened up suddenly a Miracle Mile whereon the unscrupulous could set up shop and manufacture and market their waves," he said. "People who have been flooding the market with sex novels about flappers who were lured to roadhouses found that they could write the same sex novels about the American historical scene. They had only to dress their flappers in crinolines."

Mr. Kantor was a fellow of the Society of American Historians, a member of the American Society for Psychical Research, and an honory member of the Associations of Civil War Musicians.

Apart from his interest in history and military matters, he also was interested in crime. He spent two years with the uniformed divison of the New York police department in the late 1940s, and used his experience as the basis for the novel, "Code Twenty-Three."

His children's books included "The Voice of Bugle Ann" (1935) and "the Daughter of Bugle Ann" (1953).

Mr. Kantor was born in Webster City, Iowa, on Feb. 4, 1904. He sold his first short story at the age of 17, and got his first job on the Webster City Daily News, of which his mother was editor. He later held various newspaper jobs in Chicago and contributed to a column in the Chicago Tribune. It was there he met his wife.

The couple moved to Cedar Rapids, Iowa, where Mr. Kantor worked briefly on a newspaper until it was sold. That was the last regular employment he ever held.

Although he never completed college, Mr. Kantor received honorary degrees from Grinnell College, Drake University, Lincoln College, Ripon College and Iowa Wesleyan College. He was a member of the National Council of the Boy Scouts of America and a consultant on American letters to the Library of Congress.

Besides his wife, Irene, survivors include a daughter, Layne Kantor Shroder, and a son, Thomas (Tim) MacKinlay Kantor, all of Sarasota.