Sam Spiegel, 81, the producer of some of the most admired films in the modern history of the cinema, was found dead yesterday in his hotel room on St. Martin, one of the leeward islands in the Caribbean. The cause of death was not immediately known.

Friends said that Mr. Spiegel underwent prostate surgery in London recently and that he had gone to the island to convalesce.

Mr. Spiegel's films included "The African Queen" (1953), "On the Waterfront," (1954), "The Bridge on the River Kwai" (1957), "Suddenly Last Summer" (1960), "Lawrence of Arabia" (1962) "The Swimmer" (1968), "Nicholas and Alexandra" (1972) and "The Last Tycoon" (1976).

"On the Waterfront," "The Bridge on the River Kwai," and "Lawrence of Arabia" got Academy Awards as best picture of the year.

A producer is responsible for financing a production and choosing the director and actors to execute the project. Like other producers, Mr. Spiegel did this work on his own movies. But he did it in such a way that his films bear a special mark. At their best, they transcended the screen and became the kind of event by which people keep track of their lives: remembering the first time they saw "The African Queen"; Marlon Brando saying he could have been the champ in "On the Waterfront"; the march in "The Bridge on the River Kwai" and Alec Guinness going crazy; Peter O'Toole and the incredible desert in "Lawrence of Arabia."

Mr. Spiegel was a Jew born in a part of the Austro-Hungarian Empire that is now Poland. He fled from the Nazis in Germany in the early 1930s. He first made movies under the pseudonym "S.P. Eagle." In his profession he was a gambler, a perfectionist, a taskmaster, a storyteller, a judge of character and an inspiration to some of the greatest talents in the industry.

By the account of his friend and colleague, director George Stevens, he was relentless in his pursuit of excellence.

And also by his own account. In an interview with The Washington Post in 1983, Mr. Spiegel said he had no hesitation in waking directors in the middle of the night.

"I really spent an awful lot of sleepless nights saying, 'I wish we had done this and this; let's reshoot it tomorrow.' That's part of the creation of the movie -- that you don't sleep; the night is really meant to repair the flaws of the day."

The movies he remembered best, he said, were the ones that required the largest sacrifices from himself. "Lawrence" was foremost among them.

"It took four years of my life, but without a week's vacation, without a day's vacation," he said. "It was like waging war. The places we were shooting, it was over 100 degrees in the winter. We worked in different countries, we worked in different hemispheres; in Jordan, in Morocco, in Spain.

"You had to practically carry your thousands of horses and tents and animals from one hemisphere to another. We had to decide whether one shot, like Omar Sharif coming through the haze on a camel in the wee hours in the desert -- you remember probably one of the most beautiful shots in the movie? -- whether this is worth wasting two weeks, in the hours between 3 and 4:30 in the morning till 6 to capture, this is the only time you get bits of it. This is a decision that requires enormous amounts of reflection and several other animals and other horses and other actors standing around just to get one actor and one camel approaching, and this is a thing one has to decide on the spot."

Such was Mr. Spiegel's portrait of himself at work.

In the same interview, Mr. Spiegel said that he had not "made important pictures in 10 years because I've made them all before. In a period of 10, 12 years, between 1950 and 1962, I made five or six of the most classical pictures, concentrated in a short period . . . . I lived for it, I lived in search of putting all of me into these pictures."

He was 62 years old when he finished, he said, and "an exhausted man."

At the beginning of that extraordinarily creative period, it seemed that little could stop Mr. Spiegel, least of all the lack of money.

To make "The African Queen," he took a $25,000 mortgage on his house, borrowed $50,000 more to buy the rights to the story, and set up a partnership with John Huston, who directed it. He persuaded Katherine Hepburn and Humphrey Bogart to take most of their compensation from the profits of the film. It all worked out, and so film history was made.

If Mr. Spiegel could be persuasive, he also could be persuaded. Budd Schulberg and Elia Kazan were having problems with "On the Waterfront." Schulberg had done the script and Kazan was the director. Darryl F. Zanuck was going to produce it, but he backed out at the last moment.

In an afterword to the published version of the film script, Schulberg recalled a resplendent Mr. Spiegel inviting himself and Kazan to a party. When they declined, he asked if "you boys" were in trouble. They said they were. According to Schulberg, Mr. Spiegel said:

"Why don't you come to my room tomorrow morning and tell me the story? I'll see you at seven. I'll leave the door unlocked so I won't have to get up."

The next morning, Schulberg told him what had happened with Zanuck. Mr. Spiegel had not gotten out of bed before he agreed to make the film.

Mr. Spiegel was born in Jaroslau, Poland. He received a degree in economics at the University of Vienna. As a young man he was married and divorced, and he lived for a time in Palestine. He also studied drama and wrote what he described as "a couple of very inferior plays."

In 1927, he visited the United States illegally. He was jailed for writing a check that resulted in a 25-cent overdraft on a Los Angeles bank. He also was hired by Paul Bern of MGM to make acquisitions. He soon went to work for Universal in Berlin making films for European distribution.

In 1933, he was tipped by a friend that the Nazis were after him and he fled to Vienna. He later worked in London, Paris and Mexico. At the end of the 1930s he was back in Hollywood. His first American film was "Tales of Manhattan" (1942).

In 1948, Mr. Spiegel and John Huston founded Horizon Pictures Inc. The first film Mr. Spiegel made under his real name was "The African Queen." He was renowned as an independent operator who avoided the trappings of the studio system.

In time, he became a man of wealth if not of leisure. He collected French impressionist paintings. He also had some Picassos, including one that the artist tried unsuccessfully to buy back. He maintained residences in St. Tropez on the French Riviera and in London as well as in New York.

In addition to the marriage of his youth in Vienna, Mr. Spiegel married an actress in 1957. He later married Anne Pennington, a secretary, by whom he had a son, Adam, now 17. He also had a daughter.

"Don't ask me any more questions about my marriages," he told The Post in 1983. I live alone . . . . I have substituted my emotional involvement in movies for a great many other values people treasure."