LOS ANGELES – Utility workers connected the wrong wires and caused a blackout across major portions of Los Angeles yesterday afternoon, trapping people in elevators and snarling traffic at intersections, authorities said.

About 2 million people were affected by the resulting power surge and outages, which were reported from downtown west to the Pacific Coast and north into the San Fernando Valley.

Much of the power, which failed at about 12:30 p.m., was restored within less than two and half hours; all power was expected to restored by 5 p.m.

Several workers who were installing an automated transmission system hooked up the wrong wires, according to the general manager of the Los Angeles Department of Water and Power, Ron Deaton.

“They connected it to another line that was not expecting that much electricity,” he said. No one was injured in the mishap, but officials said two workers suffered minor breathing problems when smoke backed up at an oil refinery after the outage.

Downtown high-rises went dark, fire officials said they received reports of people stuck in elevators, and stoplights went out at intersections across the city.

Neighboring cities, including Burbank and Glendale, also were affected.

The Police Department went on “full tactical alert,” meaning no officers were allowed to leave work when their shifts were over.

But calm prevailed in downtown Los Angeles, with office workers taking the opportunity for an extended lunch as police and fire sirens echoed in the background.

The blackout came a day after ABC aired a videotape of a purported Al Qaeda member making terrorist threats against Los Angeles and Melbourne, Australia, on the fourth anniversary of the September 11 attacks.

But even before the utility explained what happened, a Homeland Security Department spokesman, Russ Knocke, said there was no indication of terrorism.

Still, Mayor Antonio Villaraigosa recognized that the timing “created a heightened sense of concern.”

Some Los Angeles neighborhoods did not lose power at all.

Los Angeles International Airport lost power, but its emergency generator kicked in promptly and no flights were affected, an airport spokesman, Harold Johnson, said. UCLA Medical Center used backup generators and reported no danger to patients.

Los Angeles operates its own power utility, which serves 1.4 million electricity customers. Customers of Southern California Edison, the largest utility in Southern California, were not affected, according to spokesman Gil Alexander.