Japanese and U.S. negotiators have agreed to resume limited U.S. beef exports to Japan, but the timing remains uncertain. Beef trade was suspended, following the discovery of bovine spongiform encephalopathy (BSE), also known as mad cow disease.

American agricultural officials expressed hope that U.S. beef exports to Japan would resume within a matter of weeks. But Japanese officials, after the conclusion of bilateral talks in Tokyo, said they expect resumption of imports by July of next year.

Negotiators say they had to bridge wide differences on how strictly beef producers should test their cattle for mad cow disease.

Japan halted beef imports from the United States last December, after a single case of mad cow disease was detected in Washington State from an imported Canadian animal.

In this week's talks, Japanese negotiators were adamant about restricting American beef to that coming from younger cows. Japan has confirmed 14 domestic cases of mad cow disease, all in animals older than 20 months.

The lead U.S. negotiator, Agriculture Undersecretary J.B. Penn, told reporters here Saturday that, for the time being, U.S. exports to Japan would be limited to meat products from younger animals.

"In this agreement, the United States has agreed that we will ship only beef and products from beef animals that are 20 months or younger," said Mr. Penn.

U.S. and Japanese officials describe the three-day talks as heated. The most contentious issue was how to verify the age of cows. 

The two countries agreed to continue expert-level talks to find a way to determine cattle age, aiming for a deal within 45 days.

Japan has resisted U.S. efforts to determine age by inspecting the quality of meat and bone structure.

Japan demanded all imported U.S. beef be from animals with birth certificates. But the majority of U.S. producers do not keep such records for each animal, relying instead on herd records and a grading system that uses tenderness of the meat to judge age.

U.S. Agriculture Deputy (USDA) Undersecretary for Marketing and Regulatory Programs, Charles Lambert, says the two countries have agreed to a study, which he hopes will demonstrate to the Japanese that the USDA grading system is accurate in determining the age of meat.

"In the U.S. system, and in the world trading system, the value of about $45 billion of boxed beef every year is determined by the relative price differences in USDA quality grade," said Mr. Lambert.  "So, it is a well accepted system that is recognized worldwide."

The joint study will include experts from the World Health Organization and the World Organization for Animal Health. 

Japan has tested every domestically slaughtered cow entering the market since 2001, following the first discovery in Japan of mad cow disease. It has also banned the use of meat-and-bone meal made from cattle and sheep.

This is the top export market for U.S. beef producers, who sent $1.5 billion worth of beef a year to Japan before the ban.