Japanese officials have begun to express concern that trade problems with the United States will increase now that the presidential election is over.

Both government officials and Japanese businessmen are pointing to the mounting U.S. trade deficit as a source of increased pressure on Japan to make greater trade concesssions while at the same time adding to protectionist demands in the United States.

Reagan administration officials, however, deny any intention to attack Japan over its growing trade surplus.

Nonetheless, Japanese diplomats talk openly about the likelihood that the Reagan administration will intensify the pressure on Tokyo over the trade issue.

In Tokyo, United Press International reported that a leading economic newspaper, Nihon Keizai, echoed that view when it wrote, "It is inevitable that the U.S.-Japan trade friction will flare up again after the U.S. presidential election."

The Japanese are concerned that the Reagan administration might try to force the government of Prime Minister Yasuhiro Nakasone into trade concessions that would be politically unacceptable or impose protectionist measures that would keep Japanese products from their best market.

According to specialists here, the Japanese believe the Reagan administration downplayed potential trade disputes until after the election to keep the mounting trade deficit -- expected to reach a record $130 billion this year, $31 billion of it with Japan alone -- from emerging as a campaign issue.

With the Reagan victory, however, they expect these potential sore points to surface and see a recent speech by the highly respected U.S. ambassador to Japan, Mike Mansfield, as the first shot in the new round of trade disagreements.

"We believe that we could sell more manufactured goods and agricultural products in Japan were we given the access we seek," Mansfield said.

Reagan administration trade officials, however, said the Reagan administration has no plans to expand a host of unsettled trade issues, ranging from steel and autos to high technology, into major issues that could upset relations between the two countries.

"Trade concerns within the administration are at an all-time low," said one highly placed official.

"But the Japanese are extremely concerned," he continued. "They cannot understand that the United States is not going to do anything with such a large trade deficit."

Two U.S. specialists in Japanese trade -- Assistant U.S. Trade Representative James M. Murphy Jr. and Clyde Prestowitz, counselor to Commerce Secretary Malcolm Baldrige for Japan -- will be in Tokyo this week, and a key representative of the Ministry of International Trade and Industry (MITI), Makoto Kuroda, will visit Washington, UPI reported from Tokyo.

Imports of Japanese steel and automobiles are the high-visibility issues, with three of the four major American car makers and the United Auto Workers of America seeking a continuation of Japan's "voluntary" restraints on the number of vehicles it is exporting to the United States. General Motors Corp., with its plan to import Japanese small cars, did not join its fellow auto makers in asking for more restraints.

The steel issue is more immediate, with President Reagan committed to trying to lower imports by mid-December. But Deputy U.S. Trade Representative Robert Lighthizer was rebuffed three weeks ago when he said Japan's steel exports to the United States had surged this year and asked for substantial reductions. The talks will continue in Washington later this month.

The Prestowitz-Murphy talks, however, are likely to focus on opening Japan's market to high-technology products where the United States is believed to hold a competitive advantage and on making sure the Nakasone administration sticks to agreements to ease barriers to U.S. goods.

American businessmen, for instance, are concerned that U.S. telecommunications products could be frozen out of Japan by a proposal that places testing and certification in the hands of Japanese competitors. Much of the debate on this question is being conducted behind closed doors by Japanese bureaucrats, and the United States is pressing Japan to make the decision-making process more transparent so U.S. firms can lobby equally with Japanese companies.

The issue of "transparency" creates a major conflict between the Japanese and American ways of conducting government business. The openness of the U.S. system allows Japan to lobby the administration and Congress, while the more closed Japanese society keeps out foreign interests until it is too late.

Even opening Japan to more American products is unlikely to change two decades of Japanese trade surpluses with the United States, Commerce Undersecretary Lionel H. Olmer reported.

"Under current conditions with the Japanese market fully open, I believe the deficit would be about $15 billion to $20 billion rather than over $30 billion," he said in a report last month.