SAN SALVADOR, NOV. 20 -- Leftist rebels launched coordinated attacks against army positions in at least 11 towns around the country this morning, provoking the heaviest sustained fighting since last year's offensive.

According to Defense Minister Col. Rene Emilio Ponce, at least 25 persons were killed -- 12 government troops, 10 guerrillas and 3 civilians -- and 66 toops and 50 civilians were wounded. Among those killed was an army captain who was a key officer under investigation in last year's killings of six Jesuit priests.

A communique issued by the high command of the Farabundo Marti National Liberation Front (FMLN) rebels said the actions were a limited military campaign entitled "punishment to the anti-democratic armed forces." But in a televised broadcast tonight, President Alfredo Cristiani characterized the fighting as a "new, unjustified terrorist offensive."

The war of words over whether the fighting is limited or an all-out offensive, has important implications. Last month, the U.S. Congress, reacting to human rights violations, voted to withhold half of El Salvador's $85 million military aid package. However, the aid is to be renewed if the guerrillas launch an offensive that threatens to topple the Cristiani government.

The fighting is the heaviest since last November, when the rebels launched the largest offensive of the 11-year-old civil war, occupying large areas of the capital and other major cities. However, today's attacks appeared to be of smaller scope. The capital remained quiet.

Fighting continued through the day in three towns north of the capital. In Apopa, 10 miles from San Salvador, the rebels took over several neighborhoods and were holding their own against army counterattacks.

Civilians started fleeing the area at first light, carrying small children and bundles of belongings. They walked down the town's narrow streets waving white flags. Government troops took cover behind trees and in the doorways of houses. Occasional bursts of machine-gun fire and grenade explosions came from the rebel-held areas.

"The combat started in the early morning," said Victor Emanuel, 28, as he carried his 3-year-old son to safety. The rebels "are in the next-door neighborhood. They have set up barricades at the entrances," he said.

Rescue workers said that a large number of civilians had decided to stay. "They say that if they are going to die they want to die in their own houses," said Carlos Fuentes, 16, a worker for the Salvadoran Green Cross.

Rebel fighters in Apopa interviewed by journalists said they planned to hold their positions until they received further orders.

The heaviest fighting was reported from the eastern garrison town of San Francisco Gotera, close by the rebel mountain strongholds of northern Morazan province. Civilians contacted by telephone said that by mid-morning guerrillas had fought their way to the center of the town, where there is a large military base.

Capt. Carlos Herrera Carranza, of army intelligence, was reported to have been killed by a sniper bullet. He was one of the key officers under investigation in the killings last year of six Jesuit priests and two Salvadoran women.

Court documents indicate it was on Carranza's initiative that a search of the residence of the Jesuits was ordered three days before their deaths.

Hours after the killings, early Nov. 16, Carranza interrupted a senior intelligence meeting with the news that the Rev. Ignacio Ellacuria, a principal leader of the Central American University, was dead. In testimony, Carranza said he heard the news on commercial radio. But according to a source at the meeting, it took place before any stations started broadcasting.

Accounts today from San Francisco Gotera listed five other soldiers and two civilians killed. The radio reports said helicopters were circling the town in support of the beleaguered ground troops.

The rebels also mounted a hit-and-run attack using homemade mortars against the main military air base at Ilopango on the outskirts of the capital. An army spokesman said a spotter plane was damaged. There was fighting in the departmental capitals of Usulatan, Chalatenango and Zacatecoluca.

The guerrilla communique warned that rebels feel at liberty to launch a full offensive if there is no progress in peace talks. United Nations-sponsored negotiations have stalled over rebel demands for a short-term restructuring of the armed forces and eventual demilitarization.

The two sides are due to meet before the end of the month. In the last month, U.N. mediator Alvaro de Soto has put forward a compromise plan on the future of the armed forces, according to diplomats.