The Japanese government, prodded strongely by businessmen, today announced a broad program to stimulate its economy, including a drive to increase industrial plant exports.

The new economic program also includes a 1 percent drop in the bank rate, additional public works spending and increased aid to industries. The Bank of Japan announced its official discount rate would be lowered to 6 1/4 percent as part of the plan.

Rokusuke Tanaka, minister for international trade and industry, told a news conference that under the new program the government would, if necessary, use mixed export credits to match competitive terms supplied by other countries.

Japan's sluggish economy has begun to worry the usually buoyant economic planners, although they insist they're not faced with the serious, long-term economic malaise they see in the United States and some western European countries.

"It is not as serious as in the Western countries, but for Japan, it is serious," Isamu Miyazaki, vice minister of the economic planning agency, said recently. If some stimulation isn't applied, he said, economic growth this year might fall to between 3 percent and 4 percent, considerably below the official target of 5.3 percent established for the fiscal year beginning April 1.

Miyazaki predicted that without a new economic program, "Bankruptcies will increase, unemployment will not decline, profits will fall and people will become gloomy."

For most other countries, the Japanese economy would be a model for envy. It survived the past round of oil price increases with minimal damage and has largely overcome the big fear of large-scale inflation. After April, Miyazaki said, the annual inflation will fall to about 5 percent in consumer price increases.

But the strong recovery predicted last fall has not come about. There has been a slump in personal consumption and a deterioration in the housing industry. New investment by small and medium-sized industries has fallen, and inventories are considerably higher that they were projected to be at this point.

The business community, which is traditionally less sanguine than government planners, has been emphasizing those problems in research studies and press conferences to back up its demand for action.

Several banks and research organizations are predicting continued bad times. The Mitsubishi Research Institute has projected a growth rate of only 4 1/2 percent in the coming fiscal year. And the influential Federation of Economic Organizations recently warned of a slump in corporate earnings this month and asserted that the downturn is going to continue for some time.

Japan's normal reaction in a sluggish period is to churn up its export industries for a bigger assault on foreign markets, but that's not the case this time. In his recent interview, Miyazaki said there's not much hope for bigger exports to Western markets this year, citing the slow growth rates being predicted in the United States and Europe. Another reason, he said, is that many of those countries already are running big trade deficits, and more Japanese exports would only cause new frictions.

The one exception is the change in export assistance to boost sales abroad of industrial plants, which have not been selling well. The government will offer more appealing export-import loans and long-term, low-interest loans from the Overseas Economic Cooperation Fund. Miyazaki insists the new credit arrangements will be offered in such a way as to avoid new trade frictions and would not violate a code governing credits established by the OECD.

The emphasis, he said, will be on stimulating domestic demand in order to avoid angering trading partners. One reason for undertaking a new program is to lessen the chance that "businessmen will start pushing exports, which will cause new frictions" overseas.