LEAD: Leftist guerrillas thoroughly infiltrated a major army base before destroying it Tuesday, according to two senior military analysts here.

LEAD: Leftist guerrillas kidnapped the leading candidate for mayor of Bogota today, the police said.

LEAD: Leftist guerrillas ambushed a small navy vessel today, killing eight military men and wounding seven others, Colombian officials said.

LEAD: Leftist guerrillas kidnapped four foreigners today and took responsibility for the kidnapping of a French diplomat, officials said.

LEAD: Leftist guerrillas today released 13 of the 15 foreigners and journalists they kidnapped last week.

LEAD: Leftist guerrillas exploded bombs in the restrooms of two ministries here today, causing damage but no injuries, the police said.

LEAD: Leftist guerrillas attacked six military posts today, killing at least 12 soldiers and wounding 14, the military said.

LEAD: Leftist guerrillas attacked an army outpost early today, killing at least three soldiers and wounding five, army sources said.

LEAD: Leftist guerrillas widened their recent peace offer today by proposing a 60-day cease-fire if the elections are postponed, as the rebels suggested last month.

LEAD: Leftist guerrillas today welcomed the Government's announcement that it was willing to resume negotiations to settle the 11-year-old civil war without any preconditions.