Just when the American baseball bat makers thought they could take a swing at the lucrative Japanese baseball bat market, the Japanese have thrown a curve.

After months of haggling with the Japanese baseball leagues, which control most bat sales in Japan, U.S. manufacturers were told within the past week that they could be certified to sell bats in Japan. But now the U.S. bat makers say the Japanese have abruptly changed the specifications for foreign bats that can be sold there, requiring them to make products that will tie up production and are of lower quality.

The bat manufacturers said the last-minute changes are typical of delaying tactics used by the Japanese to keep out foreign competition. The U.S. companies said it is now too late to sell for this year's season.

"It looks like an extra cost and a crazy requirement," said George Manning, technical services manager for Hillerich and Bradsby, makers of the Louisville Slugger. "We see it as an attempt to keep us out of their markets."

"They're just playing the same game," said Fred Juer, president of Worth Bat Co. "They are going to resist in every way possible."

The baseball bat problem is a symbol of the trouble U.S. negotiators have in attempting to reduce trade barriers with Japan in agricultural, automotive and other products.

Getting a hold on the Japanese market could mean an increase in sales for U.S. manufacturers of $7 million to $8 million a year, Juer said. Although that doesn't sound like much, he said the total baseball bat market in the United States is about $30 million.

The Japanese baseball bat market consists mostly of aluminum bats used to hit rubber balls in the Japanese-style game. Japan has 1.2 million amateur players on 61,551 teams, according to the Sporting Goods Manufacturers Association.

The new specifications require the U.S. manufacturers to:

* Change the aluminum alloy they use in the bats to one long ago discarded by U.S. manufacturers as weaker than new materials, Manning and Juer said.

* Use rubber plugs in the ends of the bats. U.S. manufacturers make the bats without plugs because under certain circumstances the plugs can fly out of the bats and hit spectators, Manning said.

* Receive government safety approval, Juer said.

If the U.S. bat makers want to sell American-style bats through the Japanese leagues, the Japanese said they will have to test them and inspect every shipment that enters the country. "You know what that means," Juer said. "They leave them on the docks for three or four months and the baseball season is over."