Christopher Isherwood, 81, the noted British-American author who is perhaps best known for his 1939 semi-autobiographical novel "Goodbye to Berlin," which was made into two plays and twice filmed, died of cancer Jan. 4 at his home in Santa Monica, Calif.

His career and seemingly endless wanderings took him from upper-middle-class England to the decadent Berlin of the late 1920s and early 1930s. He witnessed war in Europe and the Far East, helped run a Quaker hostel in the United States and eventually became a denizen of Hollywood. A promising writer in the 1920s, he became a spokesman for homosexual rights in the 1970s and 1980s.

The author of plays, film scripts, and travel books, Mr. Isherwood wrote most successfully in autobiography and fiction -- and seemed to walk a razor-thin line between the two seemingly different art forms.

"Goodbye to Berlin" was one of two novels he wrote about his four-year stint as an English teacher in Berlin before World War II. In this book, he made his famous remark concerning his artistic goals: "I am a camera with its shutter open and quite passive, recording, not thinking."

The characters that "camera" captured in that novel, and in his 1935 work, "The Last of Mr. Norris," were popularized on the Broadway stage and the screen in "I Am A Camera," both starring Julie Harris, and later in the musical play and the 1972 Oscar-winning movie "Cabaret," both starring Liza Minnelli as the unforgettable Sally Bowles.

These novels, plays and movies conveyed the death throes of an already battered Germany. Weimar had failed, Hitler was on the rise, and all was not right with the world. His Berlin was a lurid city with characters who haunted the streets and cabarets.

His "I am a camera" method was just that: a method of "reporting." Some critics took it to mean a lack of feeling on Mr. Isherwood's part, but as he pointed out, he did care. He wrote not only of Germany, but of those other war-torn locales of the 1930s, Spain and China.

Mr. Isherwood returned to those times and places for his 1976 autobiographical volume, "Christopher and His Kind," which told the story of his world between 1929 and 1939. In it, Mr. Isherwood drew a frank portrait of the homosexuality he had never concealed in his private life but had not disclosed in print until the early 1970s. He also included fascinating and affectionate portraits of famous contemporaries.

The book described W.H. Auden, the famed poet who had been his lover and who collaborated with him on three plays and a travel book, on a journey to China. Auden traveled "with an immense shapeless topcoat and carpet slippers to appease his corns."

Of the writer E.M. Forster, Mr. Isherwood wrote that he "found a key to the whole art of writing," and described his friend as "a baby with a mustache." Other personalities wending their way through the book were Stephen Spender, Virginia Woolf and Somerset Maugham.

In that book and in a 1971 book on his parents, "Kathleen and Frank," Mr. Isherwood explained that homosexuality for him was not only a matter of his nature but also a rebellion against the establishment. His father, a British army lieutenant colonel, was killed in World War I, while his mother was a woman of haughty social values.

In "Kathleen and Frank" he wrote of his rebellion against the image of a hero father and all he seemed to represent, ranging from England's elitist schools to patriotism and rigid sexual morality. Mr. Isherwood acknowledged his homosexuality, became a pacifist, and deliberately flunked his exams at Cambridge University.

Mr. Isherwood once wrote that his mother, strong-willed and domineering, as well as both the church and state, endorsed heterosexuality. In "their will was my death. If boys didn't exist, I should have had to invent them."

Of all his novels, Mr. Isherwood felt his best work was his 1964 novel, "A Single Man." It is an elegant and concentrated study of a day in the life of an aging, British, homosexual don, now living near the ocean in California. Mr. Isherwood explained that its bleak and lonely outlook was not to represent only the possible plight of the middle-aged homosexual, but that of all outsiders.

"In taking up the cause of one minority, that of homosexuals against the dictatorship of heterosexuals, I have spoken out for all minorities," he told a reporter in 1978.

By the late 1970s, he was an outspoken advocate of gay rights. He told a reporter that "I think that kind of political action is one of the functions of old age. I feel it's the duty of people like me to get in the act. It seems sort of contemptible for old people not to speak up. When the hell are you going to speak out?"

Christopher William Bradshaw Isherwood was born in High Lane, Cheshire, on Aug. 26, 1904. His first novel, "All the Conspirators," published in 1928, was a critical success and commercial failure. He left Berlin in 1933 and wandered elsewhere. He came to the United States in 1939 and became a citizen in 1946. After moving to this country, he became active in the Vedanta movement of the Hindu religion and translated three Hindu philosophical works, including the Bhagavad-Gita, into English. He taught at several colleges and occasionally wrote screenplays.

He once said of himself, "My friends and acquaintances make me a rather complex creature, part despot, part diplomat . . . . Then again, I'm so sly . . . . Utterly ruthless and completely cynical. But I do make them laugh."