Lawmakers and industry groups also welcomed the news, saying it would help the United States regain access to markets that have been closed for decades.

World trade in beef was jolted in the 1980s by the discovery of mad cow disease, a fatal brain-wasting disease in cattle, formally known as bovine spongiform encephalopathy (BSE). Many nations restricted imports, some of which remain in place, out of fear of a human version of the illness.

"Making these changes will further demonstrate to our trading partners our commitment to international standards and sound science, and we are hopeful it will help open new markets and remove remaining restrictions on U.S. products," said USDA chief veterinarian John Clifford.

As an example of the new revisions, the U.S. Department of Agriculture said boneless beef could be imported because research has shown the meat poses a negligible risk of mad cow disease. Until now, imports were restricted from most nations that had reported a case of the disease.

The USDA said the new revisions, which will be published in coming days and take effect 90 days afterward, would not weaken U.S. safeguards.

"This effort is crucial to breaking down other countries' unfounded trade barriers, and re-opening trade markets that are closed to U.S. beef," said Debbie Stabenow, chairwoman of the Senate Agriculture Committee.

Stabenow said Mexico employed a non-scientific limit on U.S. cattle exports by refusing to allow entry of animals over 30 months of age. She said U.S. producers lose an estimated $100 million a year because of the limit.

The National Cattlemen's Beef Association said the new rules were "great news for the U.S. cattle industry and integral to our efforts to further expand international trade."

In a fact sheet, USDA said the changes "could convince other countries to remove any remaining restrictions on U.S. cattle and cattle products." The rules bring USDA in line with the guidelines of the World Organization for Animal Health, known by its French acronym of OIE.

On May 29, the OIE gave the United States its safest classification for mad cow, "negligible risk."

U.S. officials have struggled for more than a decade to open markets that were restricted following discovery of the first U.S. case of the disease.

The United States is among the world's largest importer and exporter of beef. Roughly 10 percent of U.S. beef is exported, while imports make up nearly 10 percent of the U.S. supply. Imports tend to be ground beef and lower-cost cuts of beef while the exports are high-value cuts.

Still, a small ranchers' group, R-CALF, said USDA said it doubted the safety of beef from Europe and called for retention of a country-of-origin meat-labeling law currently under attack in Congress.

The United States uses three interlocking safeguards against mad cow. Feed for cattle and other ruminants cannot contain "rendered" parts of ruminants. USDA runs a surveillance and testing program for mad cow. And meatpackers are required to remove from carcasses brains, spinal cords, nervous tissue and other materials that could be infected.

Mad cow, with an incubation period of years, is primarily a disease of older cattle.