WASHINGTON — Federal agents searched facilities of a dog and cat food manufacturer and one of its suppliers as part of an investigation into the widening recall of pet products, the companies disclosed yesterday.

Food and Drug Administration officials searched an Emporia, Kan., pet food plant operated by Menu Foods and the Las Vegas offices of ChemNutra Inc., according to the companies.

Menu Foods made many of the more than 100 brands of pet food recalled since March 16 because of contamination by the chemical melamine. ChemNutra supplied the manufacturer with wheat gluten, one of the two ingredients tainted by melamine used in recalled pet products.

Both companies said they were cooperating with the investigation.

Menu Foods also said the U.S. attorney's offices in Kansas and the western district of Missouri have targeted the company as part of misdemeanor investigations into whether it violated the federal Food, Drug & Cosmetic Act. The sale of adulterated food is a misdemeanor.

The FDA also is looking at all other ingredients imported by ChemNutra and trying to reconcile what it imported with what it supplied to customers, said agency spokeswoman Julie Zawisza.

Import records obtained by The Associated Press show that since May 2006 alone, ChemNutra also imported 440,000 pounds of the second suspect pet food ingredient, rice protein concentrate, from the same Chinese trading agent that handled exports of the tainted wheat gluten.

It's unknown if ChemNutra's rice protein concentrate was contaminated. Limited testing suggests it wasn't.

However, another company's imports of that same ingredient, albeit from a different source, have been found to be tainted.

Ten of the 11 containers of rice protein concentrate imported by ChemNutra over the last year went to undisclosed pet food companies, spokesman Steve Stern said.

The 11th is under quarantine and being tested. But just one of the other 10 is known to have been tested; results from those tests, done last week, showed it was not contaminated, Stern said.

The origin within China of the wheat gluten and rice protein concentrate remains murky. For example, ChemNutra's source for the two vegetable proteins, Suzhou Textile Import and Export Co., told The AP that food ingredients aren't part of its business — but that employees often take on side deals. Stern said ChemNutra dealt with the company's president.

The FDA has blocked wheat gluten imports from a second Chinese company, Xuzhou Anying Biologic Technology Development Co. That company has told AP it bought the ingredient from other undisclosed firms and then sold it to Suzhou Textile.

Meanwhile, rice protein concentrate imported by the second company, Wilbur-Ellis Co., has tested positive for melamine.

It came from a different Chinese source, Futian Biology Technology Co. Ltd.

Last week, the FDA blocked rice protein concentrates from that source. And yesterday, American Nutrition Inc. became the final of five pet food companies that Wilbur-Ellis supplied with the tainted ingredient to recall a variety of products.

An unknown number of dogs and cats have been sickened or died after eating chemical-laced pet food.

Menu Foods said it faces more than 50 lawsuits. It in turn has sued ChemNutra.