The Basque separatist group ETA this week took responsibility for a bombing in Madrid last month that killed two people. But ETA insisted that its permanent cease-fire, started last March, was still in effect. The group said it had not intended to cause casualties when it bombed a garage at the Madrid airport. It had warned the government three times to evacuate the garage, ETA said, but officials apparently overlooked the two victimsEcuadorean immigrants sleeping in parked cars. The bombing shocked the Spanish government, which called off negotiations with ETA. The Basque group has killed some 800 people in its four-decade quest for independence.