Malcolm Caldwell was a radical economist, a committed Marxist who spent his life studying and defending "national wars of liberation" in Southeast Asia.

His sympathy for the new rulers in Cambodia, his friends said, led to the invitation that cost him his life.

Mr. Caldwell was skeptical of the atrocity stories that have been attributed to the Pol Pot dictatorship. Just last summer, he wrote an article for The Times of London, "Inside Cambodia - The Other Side of the Picture." This and his other work brought a blistering attack on Mr. Caldwell by Bernard Levin, the paper's chief columnist.

When the invitation to vist Cambodia came from Phnom Penh, his friends say, Mr. Caldwell leaped at the chance to see first-hand how the new government was working.

Had he lived, this might have been his last trip to the region. "I've been caught up in Southeast Asia too long," he told one colleague.

Mr. Caldwell, born in Stirling, Scotland, was an intense Scottish nationalist and planned to devote his future energies to studies, speechmaking and pamphleteering on domestic topics.

He was 46 or 47 years old - his widow, Lynn, was not sure last night. He studied economics at Edinburgh and earned his PhD from Nottingham University

Mr. Caldwell was a lecturer in the economic history of East and Southeast Asia in the School of Oriental and African Studies at London University. There he edited the Journal of Contemporary Asia, a quarterly with a Marxist viewpoint.

His special field embraced Singapore, Malaysia and Thailand. Prime Minister Lee Kuan Yew of Singapore once blamed Mr. Caldwell for oustinghim from the Socialist International, but friends of the scholar-radical say that he had played no part in this rebuke.

Mr. Caldwell was the author of serveral books, including one on Cambodia that he wrote with Lek Tan, a fellow lecturer at the School for Oriental and African Studies.

His latest work, published this year, is "The Wealth of Some Nations," an account of what he thought was a link between underdevelopment in the Third World and "unsustainable overdevelopment" in the West.

Mr. Caldwell was described as a tall, lean man given to voluble speech. During 1965 to 1968, he was one of the most persistent speakers in Britain against the war in Vietnam.

A Friend recalled asking how he could combine his public role with his enormous consumption of books. "I spend all my nights on those trains reading," he replied.

Mr. Caldwell wa the father of four children, aged 16 to 24, by his first wife, Anne.