A blackout caused when maintenance workers inadvertently cut a power line rolled through large parts of Los Angeles on Monday, stranding people in elevators, tangling traffic, and prompting the evacuation of some high-rises and other structures.

Officials said about half of this far-flung city, served by the Los Angeles Department of Water and Power, the largest public utility in the nation, lost power starting at 1 p.m. Power was restored two hours later. Los Angeles International Airport lost its lights, but its generator kicked in, and a spokesman said no flights were delayed.

A spokeswoman for the utility said workers at a receiving station mistakenly cut one line and then hooked up the wrong wires, causing a power surge into a line that was not expecting that much electricity.

"Something was cut," said Gale Harris, a spokeswoman for the Department of Water and Power, which also lost power during the blackout. "Somebody said, 'Whoops.' "

Stranded on the street, some people expressed fears that the blackout was part of a terrorist attack. Monday's power loss came a day after ABC News, on the fourth anniversary of the Sept. 11, 2001, attacks, aired a videotape of a purported al Qaeda member threatening attacks against Los Angeles and Melbourne, Australia. The Los Angeles Police Department went on "full tactical alert," and officers were not allowed to leave work after their shifts ended. A police spokesman said terrorism was not suspected. The Los Angeles office of the Internal Revenue Service closed after a computer glitch occurred when power was restored.

The Los Angeles Fire Department reported no serious injuries.

"Our most significant calls related to this power outage have just been stuck elevators," said spokesman Ron Myers. "We're just urging people to stay put."

Long lunch breaks turned into a short workday, as thousands of workers headed home early, jamming roads already snarled with traffic.

At Grauman's Chinese Theatre in Hollywood, one of the city's landmarks, the power went out for about seven minutes, interrupting a comedy called "The Man."

"Imagine if the power had cut out when we were showing 'The War of the Worlds,' " quipped usher Lauren Fisher.

The Department of Water and Power, which serves 1.5 million customers, was one of the few utilities to emerge unscathed from California's electricity crisis in the summer of 2000. The department fought off attempts to open Los Angeles to competition from other power companies. When Enron Corp. and other companies gamed the system and prompted widespread power shortages, the department found itself in the enviable position of selling power to utilities across the state, according to James Bushnell, the research director at the Energy Institute at the University of California at Berkeley. It repaid billions of dollars of debt, and talk of further restructuring of the California energy market has been shelved.

Staff writer Sonya Geis contributed to this report.

A police officer directs traffic in Burbank, Calif., during a power outage that affected about half of Los Angeles. It was caused when maintenance workers accidentally cut a power line.