The trade deficit with Japan likely will rise to $50 billion this year from $36.8 billion in 1984, increasing pressures for protectionist legislation from Congress, Commerce Undersecretary Lionel H. Olmer said yesterday.

But the United States, in turn, is facing trade restrictions from Europe, particularly France, which Olmer said is moving to reduce competition and protect nationalized companies.

"In many European countries, there are unacceptably lengthy procedures for certification and approval of foreign telecommunications equipment," Olmer told the Foreign Correspondents Club in Tokyo. "The situation in France illustrates the disturbing state of affairs in Europe."

Moves by the United States to improve trade with Japan are proceeding slowly, and the French have reduced competition among equipment producers, Olmer said.

"At the same time, as the French market remains closed to foreign transmission and switching equipment, French firms are developing aggressive marketing strategies in the United States, recognizing that the U.S. market provides essential production economies."

However, more crucial to the world trading system is some action by Japan to open its markets, Olmer said.

"The pressures on that system are growing rapidly. Slow economic growth in most countries has increased pressures to preserve employment and protect both old and new industries. Severe trade imbalances are worsening the unemployment problems of many countries and increasing their deficits with Japan," he said.

One reason the trade deficit with Japan is expected to increase is the relaxation of voluntary automobile import quotas by Japan. That country now will ship about 25 percent more cars to the United States this year.

In large part because of the increase in car imports, the merchandise trade deficit with Japan rose to $4 billion in April from $3.2 billion in March, the Commerce Department said.

One major trade dispute between the United States and France has been over agriculture subsidies to French farmers. In addition, at the Bonn economic summit last month, France opposed setting a date for a new round of global trade talks.

The Reagan administration saw France's opposition to the trade talks as a move to stall attempts to end European agricultural subsidies.

The administration contends that these subsidies give the French and other European farmers an unfair advantage over American products in third-country markets.

"A new trade round would be useful as a pressure valve to help alleviate growing worldwide protectionist feelings," Olmer said.

"We must deal with lingering trade problems in areas like agriculture and the way in which countries protect their declining industries."