Sunthorn Kongsompong, 68, the chain-smoking general who led a bloodless coup in 1991 that toppled Thailand's civilian government, ushering in the country's last period of military rule, died of lung cancer Aug. 2 at a hospital here.

The takeover led by Gen. Sunthorn and other senior officers ended a year later, shortly after troops gunned down some 50 pro-democracy demonstrators in the streets here.

Gen. Sunthorn had since lived in obscurity. Like other figures behind the so-called National Peacekeeping Council that embodied the coup, he went unpunished for deposing Prime Minister Chatichai Choonhavan and for his alleged role in the massacre known as Bloody May.

The takeover in 1991 was the last in a score of coups or attempted coups since Thailand ended absolute monarchy in 1932. The target was the four-year-old government led by Chatichai, which was notorious for corruption.

Pledging to clean up politics, the generals set up the National Peacekeeping Council with Gen. Sunthorn, supreme armed forces commander, as chairman. But he was generally seen as a figurehead, with real power in the hands of Gen. Suchinda Kraprayoon, the army commander.

The military government proved as corrupt as the civilian administration that preceded it, and when Gen. Suchinda tried to appoint himself prime minister in 1992, tens of thousands of people poured into the streets of Bangkok in protest.

Unlike anti-government protests in the 1970s that had been led by students, these were dominated by middle-class Thais sick of graft--a constituency the government could not afford to alienate.

Masses of troops were ordered into Bangkok to restore order and ended up gunning down the unarmed protesters.

The protests were a watershed for Thai democracy. King Bhumibol Adulyadej intervened and Gen. Suchinda gave up power. Since then, the military has taken an increasingly diminished role in politics.

A civilian government was installed and four elected governments have held power since.