WASHINGTON – The government is checking a possible new case of mad cow disease, officials said yesterday, rattling the nation’s cattle industry, food processors, and beef-oriented restaurant chains.

Additional checks are being conducted after initial testing proved inconclusive on the suspect brain tissue. Officials said the animal never entered the food or feed chain.

The Agriculture Department gave no information on the location or origin of the slaughtered animal and said results from advanced tests were not expected before four to seven days.

Ranches and businesses dependent on beef are still feeling financial effects from the nation’s only confirmed case of the fatal brain-wasting disease last December.

And yesterday’s announcement sent cattle prices tumbling on fears that foreign markets would remain closed to American beef. Shares of Mc-Donald’s, Wendy’s, and other restaurant chains that feature hamburgers also slumped, as did those of American meat producers.

Mad cow disease, or bovine spongiform encephalopathy, attacks an animal’s nervous system.

People who eat food contaminated with BSE can contract a rare disease that is nearly always fatal, variant Creutzfeldt-Jakob disease.

“The inconclusive result does not mean we have found another case of BSE in this country,” said the associate deputy administrator of the USDA’s Animal and Plant Health Inspection Service, Andrea Morgan.

The “inconclusive result” was the same term the agency used in June when two potential cases turned out to be false alarms. Inconclusive results “are a normal component of screening tests, which are designed to be extremely sensitive so they will detect any sample that could possibly be positive,” Ms. Morgan said.

“USDA remains confident in the safety of the U.S. beef supply,” she added.

An industry representative seconded that view.

“Inconclusive test results are just what they sound like – inconclusive,” said J. Patrick Boyle, president of the American Meat Institute. “Regardless of the outcome of this test result, U.S. beef is safe.”

An Agriculture Department spokeswoman, Alisa Harrison, said the animal in question was among “high-risk animals” subjected to the new screening procedures. Those are animals that died on the farm, have trouble walking, or showed signs of nerve damage.

She said no quarantines have been established on slaughterhouses, feedlots, or farms. “There’s no reason to do that since it’s an inconclusive result,” Harrison said. “Should it be positive, we will be ready.”

In the only confirmed American case, a Canadian-born Holstein was found to have been infected in Washington State last December. More than 40 countries cut off imports of American beef and more than 700 additional cattle in Washington State, Oregon, and Idaho were killed as a precaution.

Many of those bans remain in place. The announcement of a possible new case comes less than a month after American negotiators reached tentative agreements with both Japan and Taiwan to resume American beef and beef product shipments.

Ms. Morgan, the USDA official, said in a conference call with reporters that she did not anticipate the new announcement would affect those negotiations because of safeguards that are now in place and because of “measures that we have already taken to date.”

Exports represent about $3.8 billion of America’s $40 billion a year beef industry. The Bush administration is working to establish a national identification system for tracking livestock and poultry from birth through the production chain.

The USDA said in a statement that information about the animal and origin would be released only if the tests come back positive. “These tests cast a very wide net and many end up negative during further testing,” the statement said.

The agency says it has performed rapid screening tests on over 113,000 cattle since an enhanced surveillance program began June 1 on cattle considered at high risk for BSE – and that this was only the third time samples had been sent on to the next level of testing.

The two earlier samples, both in June, were deemed “inconclusive,” and additional tests came back negative.