RAIN-TRIGGERED mudslides killed at least 24 people and left more than 600 homeless in mountain resorts outside Rio de Janeiro, Brazil, civil defense officials said Friday . . . A STRING of barges apparently struck and ruptured a submerged gas pipeline in the Intracoastal Waterway, near Houma, La., touching off an explosion and fire witnessed from a Coast Guard helicopter Friday. Four crewmen aboard a tugboat pushing the four barges were slightly hurt.