An attempted coup d'etat Monday that left five persons dead and shook Thailand's fragile democracy involved some of the country's highest ranking active military officers in a broader and more complex conspiracy than officially reported, according to one of the initial plotters.

The coup attempt failed, he said, when at least two key senior officers withdrew support for the plot at the last minute because of conflicts over the spoils in a future government. In bailing out, they left in the lurch a core group led by a cashiered former Army colonel, waiting in vain for anticipated reinforcements to help overthrow the government of Prime Minister Prem Tinsulanond, the source said.

The plotter, who spoke on condition of anonymity, described a web of intrigue, bitter longstanding rivalries and personal ambitions among senior military officers as factors involved in the coup attempt. He said that he had been invited to join the coup attempt by former colonel Manoon Roopkachorn but pulled out shortly before it was launched because of a conflict with one of its senior participants. His account tallied with known facts in the case and has been confirmed on essential points by other knowledgeable sources.

Among those who initially participated in the coup plot but later withdrew, the sources said, are senior officers who subsequently were credited officially with helping to put down the coup on behalf of the government.

As part of a broad cover-up afterward, these officers helped Manoon and his brother Manas, a serving Air Force wing commander, leave the country just hours after the 400 to 500 troops in their core group surrendered to government forces, the sources said. Manoon and two aides were put on a Thai Air Force plane to Singapore, where they requested visas to enter the United States. Manas was driven to the Thai-Burmese border.

According to Thai and foreign sources, high-ranking Thai authorities have asked the United States to take Manoon in, a request that Washington is considering.

The deputy Army commander, Gen. Tienchai Sirisamphan, one of those officially credited with foiling the coup, defended the decision to let Manoon and Manas go on the ground that "we had to race against time to defuse the tension" and avert further bloodshed. Lt. Gen. Picht Kullavanich, the commander of the First Army Region, which includes Bangkok, also helped facilitate the departures, informed military and civilian sources said.

The departures, and the emerging cover-up in general, have drawn sharp criticism from civilians demanding a full accounting of the coup attempt. They have pointed out that, unlike previous, largely bloodless attempts, Monday's action killed five persons, including two foreign correspondents, wounded nearly 60 others and caused serious property damage when rebel troops battled government forces with tanks, machine guns and mortars in the heart of Bangkok.

Killed by rebel tank fire were renowned Australian cameraman and correspondent Neil Davis, who served as the NBC News bureau chief here, and American sound technician William Latch.

At a funeral service for both men today, Bruce MacDonnell, NBC's general manager for Asia, called on the Thai government to arrest the members of the rebel tank crew "and those who gave them orders." He said a review of videotapes of the incident -- Davis' camera had toppled onto the pavement when he was killed but kept rolling and captured the scene -- showed that the rebels apparently fired at the newsmen deliberately.

"What we have is a pretty clear case that murder was done here," MacDonnell said in a eulogy. He also expressed outrage that the United States would consider allowing Manoon and other rebels into the country.

Associates of Manoon portrayed him essentially as a pawn in what one described as "a power play" by a disparate alliance of retired and serving senior officers against Prime Minister Prem and his newly appointed Army chief of staff, Lt. Gen. Chaovalit Youngchaiyut. Chaovalit, whose appointment is to take effect Oct. 1 as part of an annual military reshuffle, has been identified as Picht's main rival for the coveted post of Army commander when the term of the current holder, Gen. Arthit Kamlang-ek, expires next year.

The plotter who later withdrew from the coup attempt gave this account of events leading up to it: Manoon, 49, who was dismissed from the Army for helping to lead a coup attempt by officers called the "young Turks" in April 1981, told associates that he had received a go-ahead to stage another coup.

The source accepted Manoon's invitation to join the plot and was told that the core group of soldiers loyal to Manoon and Manas would be supplemented by 3,000 to 4,000 troops from other units. The plan was that, once the Prem government was overthrown, key Cabinet posts would be taken by three retired generals. Kriangsak Chomanan would become the new prime minister, Serm Na Nakhon would be deputy premier and defense minister and Yos Thephasdin would become interior minister.

Kriangsak staged a successful coup in 1977 and served as prime minister until Prem, himself a former general and Army commander, took over in 1980.

The three retired generals were with Manoon's rebels in their headquarters at the captured Supreme Command compound during the coup attempt, but senior loyalist officers asserted after the rebel surrender that they had been "forced" to join the coup against their will.

Only hours before the coup was launched, the informant said, disputes developed over who would get the posts of interior minister and Army commander, and the two key serving officers failed to provide the needed support troops. Tensions are still running high, the source said.

While much remains murky about Monday's coup attempt, the accounts of the one-time plotter and other sources make it clear that the action was not the desperate, doomed outburst of a dismissed Army officer backed by a handful of his former troops as it first appeared to be.

"This coup should have succeeded," said Sukhumbhand Paribatra, a director of the institute of security and international studies at Chulalongkorn University in Bangkok. "Why else would the old mummies come out of their tombs?" he asked, referring to the prominent retired generals who were enlisted in the attempt. "None of them is a fool. Every one of them has a lot to lose."