Nicholas Monsarrat, 69, the author of "The Cruel Sea," a widely acclaimed novel of World War II, and of several other books, died of cancer Wednesday in the King Edward VII Hospital for Officers in London.

He was hospitalized about 10 days ago after traveling to London from Gozo Malta, where he had lived in recent years.

Mr. Monsarrat was a lawyer by training, a sailor by avocation and a novelist by profession. The sea and the war, in which he rose of the rank of lieutenant commander in the Royal Navy, are the themes of several of his books.

"I'm not a stylist, perhaps, but I want to be read," Mr. Monsarrat said in an interview in The New York Times Book Review in 1956. "Every writer wants to be a success, and I think I've got something to say."

"The Curel Sea," which was published in 1951, was his first major success. It has since sold more than 11 million copies and has been translated into a score of languages. In 1953, it was made into a motion picture starring the late Jack Hawkins.

It is the story of convoy duty in the North Atlantic. Its characters are Lt. Lockhart, a green reserve officer whose background is not unlike that of Mr. Monsarrat; Cmdr. Erickson, a captain in the merchant marine in civilian life and Lockhart's skipper in the war; their ships, "Compass Rose," a corvette, and "Saltash," a frigate, and, of course, the sea itself and the hazards it holds. Corvettes and frigates were convoy escort vessels.

What Mr. Monsarrat had to say in the novel was that the sea and the war against the German U-boats for control of the sealanes would consume all those who indulged themselves in even a moment's rest from them.

Many die because they have no choice. But others perish because they are distracted or because their courage fails.Some who survive are diminished by the loss of others for whom they cared. Thus, Lockhart falls in love with a member of the women's naval reserve. They decide to marry, and she is killed when a ferry boat capsizes in a storm.

Only Erickson, who so concentrates on the war that he sleeps aboard ship while in port rather than at home with his wife, emerges seemingly unscathed.

At the time he wrote the book, Mr. Monsarrat was head of the British Information Office in South Africa, a post he held form 1946 to 1952. He held a similar position in Canada from 1953 to 1956.

"I knew that I had marvelous story to tell, if only I could get it right," he once said. "This was the Battle of the Atlantic, in which I had served for nearly five years on convoy escort, guarding more ships, dodging more hazards, standing more watches, surviving more foul weather and burying more men than should have been demanded of an amateur sailor lately graduated from a 14-foot dinghy."

Despite the book's instant success, "no doice vita ensured," Mr. Monsarrat said. "In fact, I had to run to keep up. In one 10-year period, I wrote 11 books, while taxes, debts and alimony took the place of authority (and) proved a more capricious taskmaster and remained so forever. The only dividend was freedom."

Mr. Monsarrat's other books included "The Story of Esther Costello" (1953), "The Tribe that Lost Its Head" (1956), "The Ship That Died of Shame" (1959), and "The White Rajah" (1961). He also wrote an autobiography, "Life Is a Four-Letter Word."

"The Kappillan of Malta," published in 1974, won substantial critical acclaim. It is the story of a priest, Father Salvatore, who helps the people of the island during the months of almost daily pounding they endured from the Luftwaffe in the war.

The true "hero" of the book is Malta itself, where Mr. Monsarrat took up residence for tax reasons.

His last book, "The Master Mariner," came out last year. It was the first volume of a projected two-volume of a projected two-volume work.

Nicholas John Turney Monsarrat was born in Liverpool, England, in March 22, 1910. His father was a successful surgeon and the boy was educated at Winchester, one of Britain's leading schools, and at Trinity College, Cambridge University, where he took a law degree with honors.

After working in a solicitor's office in Nottingham for two years, he gave it up and went to London to seek his fortune as a writer. He published three novels before World War II. He also wrote a play, "The Visitors," which was produced in London with Greer Garson in the lead.

Mr. Monsarrat continued writing during the war, but his work was not fiction. It described the war in the Atlantic and life aboard the escort vessels. Mr. Monsarrat himself ended the war in command of a group of three of these ships, a frigate and two corvettes. He was mentioned in dispatches for his service.

In 1945, he published "Leave Cancelled," a novel about the 24-hour honeymoon of a young officer and his bride. It met with mixed critical reaction, Jennings Rice, reviewing it in "Weekly Book Review," said it was "utterly frank without sordidness, bitter-sweet without self-pity, tender without sentimentality." Hamilton Basso, writing in "The New Yorker," said, "Needn't take up too much of our time...I felt damned embarrassed and I got no enjoyment out of listening in."

Mr. Monsarrat published several other short works about the war before "The Cruel Sea," which he once described as "a forlorn last try" to make it as a writer.

Mr. Monsarrat's marriages to the former Phillipa Crosby and Eileen Rowland ended in divorce.

Survivors include his third wife, Ann, two sons by his second marriage, Marc and Anthony, and one by his first, Max. CAPTION: Picture, NICHOLAS MONSARRAT