Lloyd Alexander, 83, a critically acclaimed fantasy and adventure writer whose coming-of-age novels use vivid action and elements of mythology to depict contemporary struggles between good and evil, died May 17 at his home in Drexel Hill, Pa. He had cancer.

Mr. Alexander wrote more than 40 books and is regarded as one of the best-known writers of juvenile fiction of the past several decades. He won over adult reviewers with cliff-hanging plots, stylish prose and believable characters that make his fanciful, long-ago settings seem plausible and relevant.

Essayist Laura Ingram, writing in the Dictionary of Literary Biography, said the books have "the special depth and insight provided by characters who not only act, but think, feel and struggle with the same kinds of problems that confuse and trouble people in the twentieth century."

He completed three major series -- the Chronicles of Prydain, which focuses on the maturity of an assistant pig keeper named Taran and is loosely based on Welsh mythology; the Westmark trilogy of political intrigue, whose main character is a printer's apprentice on the run in a corrupt European kingdom; and the Vesper Holly series, about a young Philadelphian who comes to the rescue of President Ulysses S. Grant.

Mr. Alexander won a 1971 National Book Award for "The Marvelous Misadventures of Sebastian," about a 19th-century fiddler who helps a princess defy an autocrat who wants to marry her.

He won a 1982 American Book Award for "Westmark," the debut novel of the series of the same name.

In 1969, he received the Newbery Medal for "The High King," the fifth of his six-book series, the Chronicles of Prydain. Disney made an animated film, "The Black Cauldron" (1985), from the series.

Mr. Alexander drew from Welsh mythology, notably the Mabinogion, for his Prydain Chronicles, and gravitated to Greek, Persian and Eastern tales in his later fiction, including "The Remarkable Journey of Prince Jen" and "The Arkadians."

"I used the imaginary kingdom not as a sentimentalized fairyland, but as an opening wedge to express what I hoped would be some very hard truths," he once told an interviewer. "I never saw fairy tales as an escape or a cop-out. . . . On the contrary, speaking for myself, it is the way to understand reality."

Lloyd Chudley Alexander, a stockbroker's son, was born Jan. 30, 1924, in Philadelphia and was raised in the western suburbs of Drexel Hill. He described a solitary upbringing in a family greatly affected by the Depression.

"Oh, my parents never cracked a book, just newspapers," he told the Christian Science Monitor. "But they had lots of books. They bought them at the Salvation Army to fill up empty shelves."

He found pleasure in reading works by Shakespeare and Charles Dickens and by 15 vowed to be a writer. His parents insisted on a practical job and found him work as a bank messenger. The bank became the setting for his first published novel, a satire, "And Let the Credit Go" (1955).