A public campaign aimed at promoting imports will be part of a package of market-opening measures that Prime Minister Yasuhiro Nakasone plans to announce next Tuesday, Japanese officials said today.

The campaign would try to educate consumers and companies, perhaps starting with Japan's 20 largest exporters, on the role of imports in maintaining good relations with the world, officials said. But overt incentives or punishment to enforce the program were ruled out, according to a senior official at the Ministry of International Trade and Industry (MITI).

"One can't order," he said. "We are a private business, free-market system. It would be difficult to coerce people to act uneconomically."

Still, the official hinted that the government might use indirect means of pressure, such as withholding approval for new projects, against companies that were felt not to have the proper spirit.

Ruling Liberal Democratic Party Vice President Susumu Nikaido, who briefly challenged Nakasone for the prime ministership last fall, was quoted as being highly critical of Nakasone today during a meeting of party executive officers. He was quoted as saying Nakasone should draw on party leaders' views on the issue of U.S. trade.

Nakasone's suggestions that Japan might reduce tariffs on wood-product imports, a prime U.S. objective in the talks, has led to protests within the party. The farm and forest lobby is one of Japan's strongest and many party politicians are said to have small personal holdings in forest industries.

The prime minister, responding to criticism, was quoted by the Japanese press both as saying that he had promised nothing new to Gaston Sigur, a special envoy from President Reagan who visited Tokyo over the weekend, and that he had "used his own discretion" to get the talks moving again.

Japan, with virtually no natural resources, imports great quantities of raw materials that are processed into the industrial exports that have created its trade imbalance. While the United States seeks to sell Japan more of such raw materials as food and lumber, its main effort is to open the market here to American finished goods.

The Japanese government exercises vast powers over industry through administrative guidance, a quasi-legal system of bureaucratic oversight. However, officials often say they cannot force people to buy unwanted goods.

The campaign could also be hindered by running up against the lessons of earlier government campaigns, which taught that Japan, being almost totally bereft of natural resources, must export or die.

Protectionist sentiment is running high in the U.S. Congress, due to the $37 billion trade deficit with Japan last year and a perception that Japan is not serious about reducing it.

Nakasone has repeatedly referred to the package due April 9 as a sign of Japan's commitment to face the issue. But many people here are wondering whether he is going to have substance in the package. Some analysts here think it will consist largely of a list of past steps for which the government thinks it has not received proper recognition.

MITI Minister Keijiro Murata met with Nakasone today to review the proposed import campaign and told reporters afterward that it would be detailed in the announcement next Tuesday.

As described by the government, the idea is for Nakasone to appeal to the nation to import more. MITI would follow up with meetings with executives of top companies to provide moral encouragement.

In the meantime, government funds might be used, along with money solicited from companies, to run ads in the media pitching imports as a way of making friends.