WASHINGTON — Private security guards paid little more than janitors and restaurant cooks are guarding many of the critical security sites in the United States, usually with minimal or no anti-terrorist training, an Associated Press investigation found.

The nation's security industry found itself involuntarily transformed after Sept. 11, 2001, from an army of "rent-a-cops" to protectors of the homeland. But cutthroat competition by security firms trying to win contracts with low bids has kept wages low and high-level training nonexistent.

Richard Bergendahl fights the war on terrorism in Los Angeles for $19,000 a year. Down the block from the high rise he guards is a skyscraper identified by President Bush as a target for a Sept. 11-style airplane attack.

Bergendahl, 55, says he often thinks: "Well, what am I doing here? These people are paying me minimum wage."

Security consultant Hallcrest Systems, in a January 2005 report for the Department of Homeland Security, said its experts believe that 15-20 percent of the country's private security officers protect sites designated by the government as "critical infrastructure." Major cities have a ratio of three or four security officers to each police officer, the study said.

And the industry is governed by a maze of conflicting state rules, according to a nationwide survey by the AP. Wide chasms exist among states in requirements for training and background checks. Tens of thousands of guard applicants were found to have criminal backgrounds.

A New Jersey Democratic congressman, Rep. Robert Andrews, said he's confident that lawmakers will support a bill he sponsored to upgrade the industry by requiring criminal background checks for all U.S. security guards.

"How much is it worth not to have one criminal guarding a nuclear power plant?" he asked.

Andrews said the checks will have the effect of raising pay, because they will weed out many guards whose criminal histories lead them to accept the lowest salaries.

"This is one area where doing things on the cheap is a really bad idea," Andrews said.

"A security officer is ... not trained to be a G.I. Joe," said Paul Maniscalco, a research scientist at George Washington University.

More than five years after the attacks, Maniscalco is helping to change the security guard culture. He recently developed an anti-terrorism computer course for shopping mall guards, who are being taught they now have more concerns than rowdy teenagers and shoplifters.