Japan moved a step closer to partially lifting a ban on U.S. beef imports after a government panel on Tuesday accepted U.S. assurances that a specific grade of U.S. beef would be free of mad cow disease.

The panel's decision, if accepted by the government, would clear the way for Japan to begin importing U.S. grade A40 beef, which comes primarily from cattle aged 12 to 17 months.

Panel member Akihiro Okitani, a professor at the Nippon Veterinary and Animal Science University, told reporters that there was a high probability that meat of this grade was free of mad cow disease.

Japan banned imports of U.S. beef in December 2003 after the United States discovered its first case of the fatal brain-wasting illness, known formally as bovine spongiform encephalopathy, or BSE, in a Washington state Holstein cow.

Okitani praised information that U.S. researchers provided the panel to help it make its decision.

"The U.S. researchers came up with highly reliable data," Okitani said. He added that it was now up to the Japanese government to decide whether to lift the ban on beef imports.

U.S. Ambassador to Japan Howard Baker said he was pleased the panel agreed that using the "A Maturity" grading system was an effective method of ensuring meat from animals older than 20 months of age was not exported from the U.S. to Japan.

"Now that we have finalized a major portion of the technical side of this issue, I call upon the Japanese government to work with us to expedite the remaining implementation process, so that we may all once again enjoy U.S. beef in Japan," Baker said.

Before the ban, Japan was the most lucrative overseas market for U.S. beef producers, who sold $1.7 billion worth of beef in 2003.