Alleged Unabomber Letter Prompts L.A. Airport Alert : Terrorism: FBI sets up command post at LAX and police send bomb squad after San Francisco newspaper receives missive.

The FBI late Tuesday established a command post at Los Angeles International Airport in connection with a letter received earlier in the day by the San Francisco Chronicle from a writer identifying himself as the elusive Unabomber, a federal source said.

Officials were checking mail that passed through the busy airport Tuesday and a “high-intensity” meeting was held at 7:30 p.m. at the Torrance headquarters of the Federal Aviation Administration, the source said.

The airport was put on a high-security alert, but the source said the alert applied only to packages and letters and not passengers.

An FBI task force of 150 agents reportedly has been set up to investigate the case.

A spokesman for the Los Angeles Police Department said a bomb squad was dispatched to the airport Tuesday evening, but she would not say why.

The letter received by the Chronicle stated, “I represent the terrorist group FC. . . . I plan to blow up an airliner out of LAX within the next six days.”

In recent months, the infamous serial bomber reportedly has sent several taunting letters--one to a victim, another to a Yale computer science professor and still another to the New York Times. The letters are rambling missives that use phrases from radical environmentalists and call for “the destruction of the worldwide industrial system.”

This April, in the Unabomber’s latest attack, executive Gilbert Murray was killed by a bomb that exploded at the office of the California Forestry Assn. in Sacramento.

Over the past 23 years, the Unabomber is believed to have been responsible for 16 attacks that have killed three people and injured 23 others. The targets have been diverse: Northwestern University, American Airlines, a computer rental store owner, professors of computer science and genetics, a Burson-Marsteller advertising executive and the forestry lobbyist.

The Chronicle confirmed Tuesday night that it had received a letter from a writer purporting to be the Unabomber. Matthew Wilson, the newspaper’s executive editor, would not disclose the letter’s contents but said the Chronicle planned to publish it today.

He would not confirm whether the dispatch mentioned Los Angeles or LAX. The source, however, said the airport was put on alert after receiving a call from a newspaper.