TOKYO (AP) _ Trade negotiators ended talks Friday without reaching an agreement on U.S. demands that Japan remove restrictions on imports of wood products but another round of discussions is planned.

Lumber products trade is the only unresolved issue among three areas in which Washington has been seeking to remove trade barriers under a section of U.S. trade law known as ''Super 301.''

''There are still significant differences in our positions,'' a U.S. official in Tokyo told reporters.

''We have made substantial progress on many points, but some issues remain to be discussed further,'' said a Japanese Foreign Ministry official, speaking on condition of anonymity. ''We have concluded our talks at this round after agreeing to hold another round of talks in the near future.''

The U.S. official, who also spoke on condition he not be named, said U.S. negotiators felt they could reach an agreement before June 16, when the U.S. administration is legally required to decide whether or not to take retaliatory action for foreign trade practices it says are unfair.

''I think there is momentum to resolve the negotiations. There is strong interest in a resolution on both sides,'' the U.S. official said.

Last year, the Bush administration designated Japanese trade in wood products, satellites and supercomputers as areas in which U.S. products face unfair trade practices under the ''Super 301'' clause.

The two governments recently reached agreements on greater access to Japan's satellite and supercomputer markets, but talks on lumber trade, which began Monday, faced mounting disagreement mainly because of Japan's complicated housing and construction regulations, the Japanese official said.

U.S. industry and government officials say a Japanese law banning the construction of three-story wooden apartments unfairly limits wood imports.

They also say Tokyo's product specifications and tariffs for lumber unfairly discriminate against imports of high-value finished and semi-finished wood products. By importing mainly raw timber, they say, Japan is protecting its own uncompetitive, traditional timber processing industry.

Japanese officials, however, argue that such restrictions are necessary safety precautions in earthquake-prone Japan, and thus cannot be eased unconditionally.

While traditional Japanese architecture is based on wooden construction, modern Japan has strict building codes to minimize the risk of damage and fire from earthquakes.

Wooden structures are limited by law to single-family dwellings up to three stories, and to two-story multiple family housing. Most apartment buildings in major cities are built of steel and concrete.

Officials from both sides said they felt technical questions regarding the safety of wooden housing had been cleared up. They said progress had been made in all areas of discussion, but declined to explain remaining disagreements.

The U.S. official said he expected the talks to resume ''very soon,'' but did not say exactly when or where the next round of negotiations would take place.

Last year, the United States exported $2.8 billion in wood products to Japan, mostly unfinished logs. Industry officials estimate that if trade barriers were eliminated, the market would expand by an additional $2 billion and between 17,000 to 20,000 new U.S. jobs would be created.