David Niven, 73, the British-born actor who played officers, gentlemen, lovers and thieves with a charm and lightheartedness that are sure to be remembered when many of his films are not, died yesterday at his home at Chateaux d'Oex, Switzerland. He had amyotrophic lateral sclerosis, also known as Lou Gehrig's disease.

With his savoir-faire, pencil-thin mustache and perfect diction, Mr. Niven was one of Hollywood's ideal Englishman. Whether it was comedy or farce, spy thriller or war story, an Englishman is what he played in almost 100 movies, and he played it well. If he was not a superstar in the sense that his name alone could fill a theater, it was certainly true theatergoers were glad to see him when they got there.

In 1959, he won the Academy Award for best actor for "Separate Tables," in which he portrayed a man with a fake military background. Other successes were "Around the World in 80 Days," "Wuthering Heights," "The Moon Is Blue," "The Guns of Navarone," "Death on the Nile" and three "Pink Panther" movies.

His last starring role was in "Better Late Than Never" with Art Carney in 1981. He made a brief appearance in "Trail of the Pink Panther," which was released at the end of 1982.

These and scores of other films, most of which drew scant praise from the critics and the public, made Mr. Niven a rich man. In addition to a skiing chalet in Switzerland, he maintained a palazzo at Cap Ferrat on the French Riviera.

His fortunes were increased by two volumes of autobiography, "The Moon's a Balloon," which appeared in 1971 and sold 11 million copies, and "Bring on the Empty Horses," and a novel, "Go Slowly, Come Back Quickly," which was a best-seller in 1981.

"I am a displaced Cary Grant," Mr. Niven once said. "My acting talent is extremely moderate and always called on to produce an officer, a duke or a crook. I started as a film extra and got lucky very fast. The whole thing has been such fun, I always expect a little man to tap me on the shoulder and say: 'Sorry chum, you've been found out.' "

Such was the witty, anecdotal tone of Mr. Niven's autobiographies. His novel is about Stani, the son of an American mother and a Polish father. He becomes a Royal Air Force pilot during World War II, falls in love with an English girl named Pandora and is wounded in action. She becomes a television star. Much of the book is set in scenes drawn from Mr. Niven's own life, including the "21 Club" in New York and a movie set in Mexico.

In a review in The Washington Post, Leo Braudy said Mr. Niven's autobiographies, for all their tales of scandalous and ephemeral goings-on, successfully dramatized "the pressure that Hollywood imagery brings to bear on an individual's sexual identity by its trick of transforming often involuntary personal traits into the virtually abstract features of the 'movie star.' "

In "Go Slowly, Come Back Quickly," Braudy wrote, there is "a somber sensitivity to the actual fragility of individual lives amid the disruptions of war, time and history. Stani and Pandora may seem to be the favorites of the gods, but they are hardly invulnerable and their good looks and talents no guarantee of survival in the general tumult."

The reviewer concludes that the earlier books were public autobiographies, the novel a private one.

James David Graham Niven was born March 1, 1910, at Kirriemuir, Scotland. His family were soldiers. When the boy was five, his father was killed in the Gallipoli campaign in World War I. He graduated from the Royal Military College at Sandhurst, England, and commissioned in the Highland Light Infantry. For four years he soldiered in Malta and elsewhere.

When he left the army, he went to Canada, where he was a laborer and bartender. He eventually made his way to Hollywood with the idea that he could make a living as a film extra. One of his first jobs was as an extra in "Mutiny on the Bounty." According to one story, he set foot on the "Bounty" when he visited some friends on a British warship that was in harbor, got drunk and woke up when the ship already was at sea. He was put aboard the "Bounty" as the ship passed it.

In any case, he was signed by Metro-Goldwyn-Mayer. His first role was a bit part in "Without Regret," which appeared in 1935. Other early films were "Thank You Jeeves" and "Charge of the Light Brigade," which starred Errol Flynn.

Mr. Niven and Flynn became fast friends and shared a house together. When it came to girls, Mr. Niven said in "The Moon's a Balloon" he had a "heart like a hotel." Other friends over the years were Tyrone Power, Clark Gable, Loretta Young, Cary Grant and Rex Harrison.

During World War II, Mr. Niven went back into the British army and served in a commando unit. He was released to make films supporting the war effort and received the U.S. Legion of Merit. He then returned to Hollywood.

Personal tragedy awaited him. While in England, he had married Primula Rollo. In 1946, a few weeks after she arrived in this country, she was fatally injured in a game of hide-and-seek at the home of Tyrone Power when she opened what she thought was a closet door and fell down some cellar stairs.

In 1948, Mr. Niven married Hjordis Tersmeden, a Swedish model, who survives him. Also surviving are two children by his first marriage, David Jr., a London restaurateur, and James, a New York businessman, and two daughters adopted during his second marriage, Kristina and Fiona.