Jakarta — Without warning, like the many volcanoes that dot this island, Java erupted last year with an explosion of rice.
For the first time Indonesia produced more rice than it consumed on Java, where more than half of all Indonesians live, and the shower of abundance proved almost too difficult to take after years of shortages. The government, for instance, which controls rice sales, was unable to prevent the unexpected export of rice from Java to the nearby island of Sumatra by private traders.
Poverty does not look so stark for this nation of 154 million people, three-quarters of whom still live off the land. On average, each Indonesian produced 19 percent more food in 1980 than 10 years earlier. Total rice production kept a comfortable pace ahead of population: 4.6 percent growth vs. 2 .3 percent growth. Another vital shift: The percentage of people not having enough food to eat fell from 40 percent to 15 percent of the population. The most surprising effect, which differs from other developing countries, is that rural incomes are rising slowly, a tidal swell for the economy.
These results, announced in May in a ''secret'' report by the World Bank, point to one conclusion: Indonesian agriculture has gone ''modern.'' In rice, the main staple, the percentage of farms using the new techniques of hybrid seeds, fertilizer, and irrigation has risen to 70 percent in the last decade, from 30 percent. Deftly, the World Bank gives credit to the 15-year-old government of President Suharto.
(In a curious side note: Credit also goes to a tall Texan named Hank Bechell, the man most responsible for cross-breeding the first successful ''miracle rice'' two decades ago near Manila. He finished up his research in Indonesia just a few months ago, leaving for the United States just as Indonesia was green with success.)
But no one in Indonesia is complacent. Some agricultural specialists say the good harvests of the last two years (10 percent and 13 percent increases) may have been due to good weather. If the ''green revolution'' is here to stay, it will be seen by year's end: A mild drought has hit Java in recent months.
Another concern lies in the new seeds. They are almost all of one type, a species known as ''IR36.'' Scientists say it may just be a matter of time before this monoculture gets hit with a pest or disease, bringing the nation to sudden famine. ''The vulnerability is dangerous,'' a US official says.
And ironically, the average farm size has been shrinking, down to an acre, while the number of landless farm workers has increased by 2.2 percent. Indonesia still imports rice to make up for maldistribution and keep prices stable. In fact, imports may be on again and off again in this decade.
The Java countryside shows all of the signs of modern agriculture: Toyota tractors in the fields, Toyota pickups and motorcycles on new highways. The new confidence of farmers in modern methods may bring a rush of mechanization, such as the use of sickles for harvesting instead of the ancient ''ani-ani'' knife (which is cupped by the hand so that the rice goddess is not offended).
Mechanization will only worsen an already bad labor problem, with 20 million new workers expected in this decade. Indonesia remains a poor nation, even though the World Bank has ''graduated'' it to a middle-income country with an average $600 in earnings a year per person. The gain is mainly from oil money going to the government.
Less than 10 percent of villages have electricity, and health care remains highly inadequate. Primary education is now almost universal, but the dropout rate after the fifth grade is about 30 percent. (Afternoon classes are being tried so that children can help on the farm in the morning.)
Despite bureaucratic problems, constant corruption, and conservative peasantry, the government has managed the progress well. To consolidate its gains, the next step is the massive spreading of cooperatives. One example is a recent program, known as INSUS, in which groups of farmers are awarded prizes for highest harvest yields.
Cooperatives up to now have been government-run and badly managed, the World Bank finds. And they only served the purpose of purchasing farmers' rice. Just how to spark a true grass-roots cooperative movement, with natural marketing controls, remains a problem, even though the government plans to spend $4 billion on them in the next five-year plan (1984-88).
Another ambitious tool for keeping the pace of agriculture is transmigration, an old Dutch program of moving people off the overcrowded islands of Java and Bali to the outer islands. The present five-year plan has greatly stepped up the pace of this transfer, with the goal of 2.5 million people by 1984. After a slow start, the new settlements seem to be working, with once-landless farmers getting their own soil.
Although still a food-deficit nation, Indonesia no longer battles hunger. Instead it struggles with pushing diversified crops and balancing urban and rural interests with prices and subsidies.