WASHINGTON — Importers have learned to evade close federal scrutiny of the food they ship into the United States, putting consumers at increasing risk, congressional investigators said yesterday.

Lawmakers also criticized the Food and Drug Administration's plan to close half of its laboratories. They questioned whether it would save money and enhance the agency's ability to target unsafe food, as FDA commissioner Dr. Andrew von Eschenbach said it would.

"FDA's ill-conceived decision to close seven of its 13 laboratories likely would expose American consumers to even more danger from unsafe foods, particularly imports," said Rep. Bart Stupak, D-Mich., at a hearing of a House Committee on Energy and Commerce subcommittee.

Von Eschenbach said the lab plan was meant to modernize the FDA's food safety efforts.

The FDA's ability to police the nation's food supply has come under criticism from Congress and others amid a string of high-profile cases of foodborne illness, including E. coli-tainted spinach and salmonella-contaminated peanut butter and snack foods, as well as concerns about drug-laced, farmed fish imported from China.

An Energy and Commerce Committee investigation found the FDA now has little ability to police imports. In San Francisco, for example, the FDA's staff can conduct only a cursory review, generally dedicating just 30 seconds to each shipment as it flashes by on a computer screen, according to investigators.

Even when products are flagged by the FDA, importers have learned to manipulate the system, investigators said. For example, the FDA relies on results obtained from private labs, but those labs produce results driven by financial rather than scientific concerns.

Investigative counsel Kevin Barstow said he was told by an unnamed FDA deputy lab director that "none of the test results he's seen are completely accurate."

"The words he used were 'not good' and 'spooky,' " Barstow said.

Importers also can reduce the level of scrutiny by having their products test negative five consecutive times, according to the investigators. Since some large fish, including tuna, can be flagged for high mercury levels, importers will arrange to have five lots of smaller fish — generally younger and with less mercury — tested to obtain an all-clear from the FDA. Once the monitoring decreases, the importers can then resume bringing in larger fish that otherwise might not pass muster.

Some potentially problematic seafood imports are being steered to enter the country in Las Vegas to avoid the scrutiny they might receive in San Francisco and other West Coast seaports, according to Nelson and other investigators.

The problems go beyond food. In Puerto Rico, investigators learned importers were getting around the FDA's blocking of imports of Chinese-made toothpaste made with an antifreeze ingredient by co-packaging them with toothbrushes. Examples of the tainted toothpaste included a Crest knockoff called "Crust," he added.

The decision to close and consolidate labs is likely to have a negative impact on safety, said B. Belinda Collins, the FDA's Denver district director. Furthermore, the reorganization would likely force many employees to retire or leave, said Carol Heppe, who faces the loss of her job as the FDA's Cincinnati district director.

"This will result in a mass loss of institutional knowledge and expertise at a time when the agency is trying to be proactive in our operations to prevent more emergencies," Heppe said.

Several of the most recent and high-profile food scares have involved imports from China, including deadly pet food ingredients spiked with industrial chemicals, farmed fish laced with antibiotics and snack food seasoning contaminated by salmonella.

"We know that we are vulnerable to harm from abroad where rules and regulations governing food production often are more lax than they are at home," said Rep. Marsha Blackburn, R-Tenn., in raising the prospect of terrorists tampering with imported food entering the U.S.

Rep. Henry Waxman, D-Calif., said Congress shared some of the responsibility for the problems with food safety since it hasn't given the FDA enough money or power.