Sinhalese extremists killed at least 55 people in the bloodiest slew of attacks of their drive to topple the government and derail a Dec. 19 presidential election, officials said Monday.

At least 12 rebel suspects also were found dead.Police and military officials said the slayings occurred between Sunday morning and Monday morning and most were in the two southern districts of Galle and Matara, strongholds of the Janatha Vimukthi Peramuna (JVP), or People's Liberation Front.

Early Monday, an unknown number of JVP militants hurled grenades into the home of M. Somatunga, a former urban council chairman of the ruling United National Party (UNP), in Poranba, about 55 miles south of Colombo.

The assailants then shot and stabbed to death Somatunga and seven members of his family, officials said.

A supporter of the UNP and two members of his family died in an attack in a nearby village, they said.

At least 45 other people were slain in separate JVP raids, including two local government administrators and a state bus depot manager, officials said.

It was the highest 24-hour death toll yet in the extremists' drive to oust the government of President Junius Jayewardene through violence, sabotage, intimidation and protests that have paralyzed essential services, commerce and the administration of many areas dominated by the island's ethnic Buddhist Sinhalese majority.

JVP notices containing death threats circulated Monday afternoon within the Ministry of Public Administration, which oversees state-run industries and enterprises, prompting a walkout by hundreds of employees, officials said.

The government declared as "essential services" the Finance Ministry, crippled by a JVP-instigated walkout that started Friday, and the telecommunications system. The declaration requires employees to report to their jobs or risk being fired.