The Reagan administration plans to declare a limited success in talks to open Japanese markets to American products while insisting that more progress is needed, administration sources said yesterday.

Negotiators are now engaged in a major wrangle over the wording of a joint statement on a full year of intensive, and often bitter, trade talks ordered after a meeting last January between President Reagan and Prime Minister Yasuhiro Nakasone.

The statement summarizing the results of the negotiations is to be issued here tomorrow by Secretary of State George Shultz and Foreign Minister Shintaro Abe, who were put in charge of the talks, which focused on opening Japanese markets in telecommunications, sophisticated electronics, forest products, and medical equipment and pharmaceuticals.

The talks are the central element of the administration's strategy regarding Japan's growing trade surplus with the United States, estimated at $50 billion last year. The talks are aimed at ending what is seen here as unfair trade practices by Japan that block sales of competitive American products.

U.S. officials said the talks succeeded beyond expectations in opening Japan to sales of medical-pharmaceutical and telecommunications products, with a breakthrough yesterday in Tokyo clearing the last major hurdle in the telecommunications sector.

But they said they want the joint statement to reflect the deep disagreement between the two nations on ending Japan's high tariffs that block sales of U.S. lumber products and on what are seen here as Japanese restrictions on sales of satellites and semiconductors.

Congress and private trade circles have expressed concern that the administration would try to declare a victory in all four sectors to lessen trade tensions and help overall U.S.-Japanese relations. But administration sources said they want the statement to be "honest and factual, telling where advances are and where there are problems."

Japan, however, is balking at including the areas of disagreement, U.S. officials said. The Japanese were reported to be concerned about publicly embarrassing bureaucrats in the two ministries where successes were not achieved -- International Trade and Industry and Agriculture -- while in effect praising the work of the Ministries of Health and Post and Telegraph, U.S. sources said.

The Japanese also would like to end the talks, called "MOSS" for "market-oriented, sector-specific" negotiations. The Reagan administration insisted at a plenary session yesterday that they should continue in the areas of forest products and telecommunications, and that agreements in the other sectors should be monitored to make sure they are followed. In addition, the U.S. side wants to add more sectors in a new series of talks.

"MOSS is going to continue, and it is going to take on new sectors," one administration trade official said. This was made clear to the Japanese yesterday, he added, and they "reluctantly will go along with that."

The series of talks, which were held in Hawaii and Tokyo during the past year, cost the government an estimated $500,000 in travel, hotels and other expenses. Translations alone cost a minimum of $60,000.

The telecommunications sector got the most attention at first, working under an April 1, 1985 deadline to get new regulations in place at the same time that Nippon Telegraph & Telephone changed from a government monopoly to a private company. Since the agreement on the first phase of the telecommunications talks, 77 new American products have been certified for sale in Japan, and the agreement yesterday opened the door for future sales.

American drug companies and medical equipment manufacturers achieved major gains in ending a series of rules that for decades had blocked sales of their products in Japan.

The electronics sector is stuck over the issues of semiconductors, bars to purchases of U.S. satellies by the government to protect Japan's infant space industry and "business practices" that effectively keep Americans out of the market.