WASHINGTON — A Kansas meatpacker sued the government yesterday for refusing to let the company test for mad cow disease in every animal it slaughters.

Creekstone Farms Premium Beef says it has Japanese customers who want comprehensive testing. The Agriculture Department threatened criminal prosecution if Creekstone did the tests, according to the company's lawsuit filed in U.S. District Court in Washington.

"We're not in any way saying that U.S. beef isn't safe; we believe it's the safest beef supply in the world, but that's not the issue," chief executive John Stewart said at a news conference.

"We're talking about consumers, and consumers want the product tested," Stewart said.

Testing for mad cow disease in the United States is controlled by the department, which tests about 1 percent of the 35 million cattle, or about 350,000, that are slaughtered each year. The department is planning to reduce that level of testing.

Stewart said he was surprised at the plan to scale back testing. "Given the concerns internationally, I'm not so sure that's the right thing to do."

Private companies certified by the department make screening tests used to detect mad cow disease. The department says it has sole authority over the sale and use of the tests.

Department officials say they oppose 100 percent testing because it does not ensure food safety. The disease is difficult to detect in younger animals, which are the source of most beef.

Larger meatpackers worry that insistence from Japanese buyers would force them to do testing and that a suspect result might scare consumers away from eating beef.

It would cost about $20 per animal to do the tests, adding about 10 cents per pound to the cost of meat, according to Stewart.

Japan tests nearly all its cattle for mad cow disease. While individual companies there may want more testing in the U.S., Japan's government is not asking the U.S. to do the same.

For now, Japan has halted American beef shipments because inspectors in January found cuts of U.S. veal containing backbone, which is banned in Japan even though it's eaten in the U.S.

Japan had only recently lifted a ban on American beef imposed after the first U.S. case of mad cow disease in 2003. Until then, Japan was the top foreign buyer of American beef, accounting for around $1.4 billion in sales in 2003.

Creekstone cut production and laid off about 150 employees at its Arkansas City, Kan., plant because of the ban.

Stewart said Creekstone's customers understand the limitations of the tests. He added that he expects Japan to reopen its market regardless of whether Creekstone is allowed to test its cattle.

The medical name for mad cow disease, a brain-wasting ailment, is bovine spongiform encephalopathy, or BSE. In people, eating meat products contaminated with BSE is linked to more than 150 deaths worldwide, mostly in Britain, from a deadly human nerve disorder, variant Creutzfeldt-Jakob disease.

There have been three cases of mad cow disease in the U.S. The first, in December 2003 in Washington state, was in a cow that had been imported from Canada. The second, last June, was in a Texas-born cow. The third was confirmed last week in an Alabama cow.

Japan has had two dozen cases of BSE.