Precaution Increased at Airport : Security: Travelers advised to arrive early at John Wayne, where guards are requiring photo IDs in wake of Unabomber threat. Carry-on luggage is subject to examination.

As airports throughout California reacted to the terrorist threat by the elusive Unabomber, officials at John Wayne Airport dispatched private guards and sheriff’s deputies, warned travelers to arrive at least two hours early, and asked for photo identification even as passengers boarded planes.

The threat that a bomb would explode aboard an airliner at Los Angeles International Airport before the Fourth of July triggered orders from the Federal Aviation Administration for the heaviest security measures at John Wayne Airport since Desert Storm in 1991, said airport spokeswoman Pat Ware.

Late Wednesday, The New York Times said it received a letter in which the Unabomber took responsibility for the bomb threat and said the whole thing was a ruse.

But earlier Wednesday, Ware said officials at John Wayne were “encouraging everyone to come to the airport with a picture ID such as a driver’s license. At any time while you are in the complex, your carry-on baggage is subject to inspection.”

Several airlines were offering refunds or alternate travel dates to passengers with tickets to Los Angeles International Airport, or, in some cases, to any California airport.

Because of the need to check picture identifications, lines were longer at some ticket counters, airlines warned. But Delta Airlines station manager John Ohle estimated the delays at only 10 to 15 minutes.

Some airlines were not allowing curbside check-ins but requiring passengers to take their luggage to the ticket counter for check in, Ware said. Those accepting curbside check-ins were requiring photo identification.

Passengers with only carry-on bags were being stopped and asked for photo IDs at the tunnels that lead to the airplanes.

Lt. Dennis Rohn, in charge of the sheriff’s bureau at the airport, said he brought in three extra officers for a total of 16 to increase law enforcement visibility at the metal-detection checkpoints and outside skycap check-in areas at the terminal’s upper level.

“We want to be more visible and closer at hand to be of assistance to the public and to the airlines if they need us,” Rohn said. “If a suspicious item is located, we take over from there.”

All unclaimed luggage found at the airport was being examined, Rohn said.

David Mazer, a spokesman for the U.S. Postal Service, said that only letters and parcels weighing less than 11 ounces were being put aboard airliners for delivery. He said the bomb threat affected at least 400,000 pieces of mail with California addresses Wednesday.

“We’re accepting mail at John Wayne and working out plans for heavier parcels,” Mazer said. “Incoming mail is not a problem because it’s already been checked. But outgoing is.”

The terrorist threat resulted in “a few dozen” passengers who were scheduled to land at LAX switching plans at the last-minute to land at John Wayne Airport, Ware said. But no flights were canceled.

Travel agents said the Unabomber’s threats were the talk of the industry Wednesday, but clients booking flights did not express much concern.

“We braced ourselves for phone calls, and it just hasn’t happened,” said Denise Vaccaro, who owns Capistrano Travel in San Juan Capistrano. “But that may be because a lot of people are at work and they haven’t heard about the threat yet.”

With both short-term and long-term parking lots nearly full Wednesday, Ware recommended that travelers park at the airport’s Main Street parking lot between MacArthur Boulevard and Red Hill Avenue, where they can get a shuttle every 15 minutes.

In the terminal Wednesday, the airport’s loudspeaker repeatedly broadcast this additional warning: “All passengers are advised to control their baggage and packages, to avoid transporting items without their knowledge . . . and [to] report any suspicious bag, parcels or other items to law enforcement and other airline personnel.”

Beverly Ward didn’t know about the threat when she arrived at John Wayne on Wednesday. But when she called her mother and learned about it, she stayed calm.

“I work for the federal government, and it happens all the time,” Ward said. “I guess I’m just desensitized.”

Paul Larson, who had just arrived from Texas, said he had reservations to fly out of LAX today. The Texan wasn’t worried.

“No ma’am, I’m not afraid . . . it’s California.”

Times staff writers Leslie Berkman and Phuong Nguyen contributed to this story.