Washington ? There is a “high probability” that more American cattle are infected with mad cow disease than the one found in Washington state late last year, an international panel of experts convened by the Agriculture Department said Wednesday.

The panel concluded that the mad cow agent, which came initially from Canada or Europe, has probably spread within the American beef herd. The advisory group also said the American government and beef industry must do more to keep it contained.

The head of the panel, Swiss professor Ulrich Kihm, told reporters that based on his experience in Europe, the United States may see as many as one new mad cow case per month in the future.

The panel report was immediately attacked by the National Cattlemen’s Beef Assn., which called it “misguided” and “nonscientific” and based on European circumstances very different from those here. USDA officials stressed that even if more infected cattle are found, procedures in place will keep the contaminated beef out of the food supply.

The USDA commissioned the panel to analyze the response to the first known American case of mad cow disease. It now goes to a standing advisory panel before being presented to Agriculture Secretary Ann Veneman for possible action.

The report’s central conclusion is that “it is probable that other infected animals have been imported from Canada and possibly also from Europe.” Because those infected cattle weren’t detected, the experts said, their contaminated parts have been rendered and possibly fed years ago to cattle and other animals here, eventually spreading through the American cattle population as a whole.

The expert panel made recommendations it said were necessary to keep the disease from spreading — some involving significant changes to current American policy. The group said, for instance, that the government must ban the feeding of beef brains and central nervous system tissue to pigs, poultry and pets. The Food and Drug Administration prohibited the feeding of cattle parts to other cattle in 1997 and recently broadened the ban to include goats and sheep. The panel said Wednesday the ban should cover all animals because of the risk of infected tissue inadvertently making its way into the feed given to cattle.

Industry officials said meeting that standard would cost $700 million a year.

The panel also recommended significantly expanding the testing for animals showing any signs of mad cow disease. The USDA now tests a sample of animals that have died on the farm, can’t stand up or show signs of neurological disease. The panel said that all animals in those categories — which beef industry officials say could number as many as 195,000 a year — should be tested.

“Now that it has been established that the (mad cow) agent is circulating in North America, the surveillance program in the USA must be significantly extended in order to measure the magnitude of the problem,” the report said.