Lon Nol, 72, the U.S.-supported general who came to power in Cambodia by overthrowing the government of Prince Norodom Sihanouk and was later himself deposed by the communist Khmer Rouge, died yesterday in Fullerton, Calif., where he had been living in exile.

As a soldier and civil servant for more than 40 years, Lon Nol figured prominently in the confused and confusing tangle of political maneuvering, of coup, insurgency and countercoup connected with the long years of war in Southeast Asia both before and after the American involvement there.

His 1970 ouster of Sihanouk, who had been considered a neutralist, has been described as the event that brought the war in Vietnam spilling across the borders of his own country, which had been relatively peaceful and self-sufficient.

He was connected with some of the most controversial aspects of America's conduct of the war, including the so-called Cambodian incursion in April 1970, and he was sustained by American aid that in early 1973 flowed to his nation at the rate of $5 million a week.

An introverted chain-smoker who wore an almost constant smile, Lon Nol practiced a style of leadership that bemused western reporters. Shunning newspapers, radio, television and telephones, he received no regular news briefing, gave credence to demons and spirits and heeded the advice of astrologers.

His defeat in 1975 and his subsequent flight to the United States was followed in Cambodia by years of slaughter under the ferociously brutal regime of Pol Pot in a tragic period chronicled in the recent film "The Killing Fields."

Lon Nol, who came to California's Orange County in 1979 after four years in Hawaii, had been in ill health since suffering a stroke in 1971. The cause of death was listed as an apparent heart attack.

Paramedics were called to his home about 4:30 a.m. Pacific Standard Time after he complained of chest pains. He died less than six hours later at St. Jude Hospital.

In one of his last prominent public appearances, Lon Nol, then partially paralyzed, came to Washington in 1978 to ask for international support in evicting the Pol Pot regime from the United Nations. The Khmer Rouge were later driven from Phnom Penh, the Cambodian capital, by the Vietnamese.

A Buddhist of partly Chinese ancestry, Lon Nol was born in the southern province of Preyveng, near the Vietnamese border, on Nov. 13, 1913. His father, Lon Hin, was a minor government official in the provincial capital.

After completing studies in a French colonial secondary school in Saigon, Lon Nol entered the civil service, rising quickly through police and administrative and military posts. As a supporter of Sihanouk he was rewarded with cabinet posts.

After economic conditions deteriorated as a result of North Vietnamese encroachments originally sanctioned by Sihanouk, Lon Nol took office as Sihanouk's premier, endowed with substantial power.

In what was viewed as an effort to win American backing, the anticommunist Lon Nol agitated against Sihanouk's alleged tolerance of both North Vietnamese and Viet Cong forces in Cambodia.

On March 18, 1970, the National Assembly voted out Sihanouk and installed Lon Nol in his place.

On April 30, 1970, President Nixon announced that U.S. and South Vietnamese forces had crossed into Cambodia to destroy North Vietnamese sanctuaries. The announcement, coming against a background of broad opposition in the United States to the Vietnam war provoked widespread demonstrations, particularly on college campuses.

In Cambodia the response was different. Lon Nol appealed to the racial and religious pride of the Khmers, Cambodia's principal ethnic group.

He called for a holy crusade of his country's Buddhist faithful against the North Vietnamese, whom he termed communist atheists.

Enthusiastic but untrained Cambodians rushed to ther front wearing amulets and scarves rather than combat boots or helmets.

The following year, after suffering the stroke that partially paralyzed his left side, Lon Nol abandoned office for a time, but soon returned. U.S. officials became increasingly involved in offering advice and aid.

Meanwhile, the United States was secretly bombing targets in Cambodia in a controversial effort that President Nixon later said was designed to help Lon Nol, but which critics said helped destabilize the country and bring about his downfall.

The raids ended in 1973. Most North Vietnamese and Viet Cong forces left Cambodia. But the Khmer Rouge, Cambodia's own leftist insurgency, continued to grow, aided by government inefficiency and failures.

By 1974 they operated in division strength and on New Year's Day 1975 communist forces launched an offensive that in 117 days of fierce fighting destroyed Lon Nol's Khmer Republic. Lon Nol fled on April 1, and Phnom Penh fell on April 17.

Several hundred thousand Cambodians were believed killed in the fighting between Lon Nol's government forces and the Khmer Rouge.

Estimates of the number of people who died under the Khmer Rouge regime range from 1.5 million to 3.5 million.

Lon Nol is survived by his wife, Sovanna, five sons, four daughters and six grandchildren.