IRVINE, Calif. — A heavy police presence blocked off a street in a typically quiet Southern California suburb Sunday, as residents adjusted to life in the midst of a huge search for a fugitive whose police and military background and vitriolic online manifesto has put the region on high-alert.

Police are working to protect dozens of families considered targets based on Christopher Dorner’s Facebook rant against those he held responsible for ending his career with the Los Angeles Police Department five years ago.