LOS ANGELES - The same food safety net that couldn't catch poisoned pet-food ingredients from China has a much bigger hole.

Billions of dollars' worth of foreign ingredients that Americans eat in products ranging from salad dressing to ice cream get a pass from overwhelmed inspectors, despite a rising tide of imports from countries with spotty records, according to an Associated Press analysis of federal trade and food data.

Well before contaminated shipments from China killed 16 cats and dogs and sickened thousands more, government food-safety task forces worried about the potential threat to humans - ingredients are hard to quarantine and can go virtually everywhere in a range of products.

When Food and Drug Administration inspectors at ports and border checkpoints look, they find shipments that are filthy or otherwise contaminated. They rarely bother with them, in part because ingredients aren't a priority.

Because these oils, spices, flours, gums and the like have not been blamed for killing humans, safety checks before they reach the supermarket shelf are effectively the responsibility of U.S. buyers. As the pet deaths showed, that system is far from secure.

Meanwhile, the ingredient trade is booming - particularly since 2001, when the Sept. 11 attacks focused attention on the security of the nation's food supply.

During the last five years, the AP found, U.S. food-makers prospecting for bargains more than doubled their business with low-cost countries such as Mexico, China and India. Those nations also are responsible for most shipments that fail the limited number of checks the FDA makes.

"You don't have to be a Ph.D. to figure out that . . . if someone were to put some type of a toxic chemical into a product that's trusted, that could do a lot of damage before it's detected," said Michael Doyle, a microbiologist who directs the University of Georgia's Center for Food Safety.

Doyle sat on several federal task forces studying threats to U.S. food security; while they discussed ingredients, he said, their findings are classified.

Read down almost any food package's label and there they are: strange-sounding substances that keep soft drinks fizzy, crackers crispy, and sauces from gooing up. Gum arabic, extracted from acacia trees, helps give light whipped cream its texture; maltodextrin is derived from starchy foods, then can be dusted on chips so spices stick; caseins, a protein from milk, help the consistency of cheese substitutes.

While Americans are consuming more imported food and drink, from preserved fruit to coffee, demand among U.S. food-makers for overseas ingredients is increasing even faster.

In 2001, the United States imported about $4.4 billion worth of ingredients processed from plants or animals, AP's analysis shows. By last year that total had leaped to $7.6 billion - a 73 percent increase. Other food and drink imports rose from $38.3 billion to $63 billion - up about 65 percent.

No single reason explains the increase. Profits are one factor; changing consumer tastes play a role, too. There's a growing expectation that seasonal products will be available year-round, immigrants may hanker for familiar flavors, and other consumers want variety.

So U.S. food-makers head overseas, where labor-intensive ingredients can be cheaper to produce in low-wage countries. They are not expensive to ship, either, because they are relatively compact and don't spoil easily, said David Closs, an expert in global food supply at Michigan State University.

By its own latest accounting, the FDA had only enough inspectors to check about 1 percent of the 8.9 million imported food shipments in fiscal 2006. Topping the list were products with past problems, such as seafood and produce.

"I don't ever remember working on ingredients," said Carl R. Nielsen, a former FDA official whose job until he left the agency in 2005 was to make sure field inspectors were checking the right imports. "That was the lowest priority, a low priority."

Today, a House Energy and Commerce subcommittee will hold a hearing on the FDA's oversight of the food supply, with a focus on the recent cases of contaminated spinach, peanut butter and pet food. The hearing is part of a broader investigation by lawmakers into the FDA's handling of food safety.