MADRID, DEC. 11 -- A car bomb apparently set by the Basque separatist organization ETA today blew up a barracks of the paramilitary civil guard corps in the northeastern city of Zaragoza, killing 11 persons, including women and children, and injuring 40.

The blast ended a six-month lull in major terrorist attacks in Spain and followed both police successes against ETA and exploratory cease-fire talks with the separatists.

Four girls -- a 7-year-old, a 6-year-old and 4-year-old twins -- were among the dead under the rubble of the three-story brick building that housed 30 civil guardsmen and their families. An estimated 110 pounds of explosives ripped a 15-yard hole in the building's living quarters and brought all three stories to the ground.

Sentries said two men parked the car against the building shortly after 6 a.m. and then sped away in a waiting car. The parked vehicle exploded almost immediately and a sentry who was approaching it for inspection was among those seriously injured.

The violence recalled ETA's last major attack in June when the separatists detonated a bomb in a Barcelona supermarket that killed 21 persons. ETA, an acronym from the Basque title Homeland and Liberty, also struck in Zaragoza at the begining of this year when a car bomb killed an Army major and a driver in a passing military bus.

Over the past two decades, ETA, one of Western Europe's most durable terrorist groups, has been linked to about 550 deaths and more than 400 of the organization's members are in prison. Avowedly Marxist-Leninist in its ideology, ETA rejects the quasi-federal status that the Basque provinces of northern Spain obtained with the onset of democracy in the nation and seek to create an ethnic Basque independent state.

Today's attack served notice that the separatists remain in the fray despite the apparent progress of the Madrid government's carrot and stick approach to curtail ETA and end the violence.

The policy involves simultaneous police drives against ETA and covert negotiations to bring about the organization's surrender. Spain has been aided by cooperation from France in the control of terrorist suspects. Algeria also has acted as host for discreet ETA-Spanish meetings.

The capture of ETA's alleged military commander in September in southwest France prompted a roundup of more than 100 suspects in Spain and France, a traditional hiding place for separatists until recently. In the past 18 months, about 160 ETA members living in France's border area have been handed over by French security officers to their Spanish counterparts.

Earlier this month, Spanish authorities revealed that a series of arrests of ETA members in Spain had thwarted a plan to bomb a ski resort where Spain's King Juan Carlos spends his winter holidays.

Officials recently have acknowledged the Algeria talks, which hinge on a separatist cease-fire and individual pardons for jailed ETA members.

Following the Zaragoza blast, a government spokesman said the talks cannot continue while there is violence.

Officials have warned that ETA hard-liners, opposed to any form of negotiation that could lead to ETA's surrender, would mount a violent attack in order to torpedo the Algerian contacts.