President Carter arrived to a royal Spanish welcome here Wednesday and warned that the West faces "a strategic challenge of historic magnitude" because of the Soviet invasion of Afghanistan. Speaking in Spanish at a luncheon given by King Juan Carlos, Mr. Carter paid credit to Spain's democratic progress since the end of the Franco era.
Just hours before Mr. Carter's arrival here, Basque guerrillas exploded four bombs in Alicante, a resort province, and assassinated a tire company executive. The guerrillas want release of 19 comrades and a referendum on the future of the part-Basque province of Navarre. No casualties were reported. The violence did not reach Madrid.