Despite having one of the more active family-planning programs in Southeast Asia. Indonesia is expected to double its population to 250 million by the year 2000. After that, it's anyone's guess.

Projections for a century from now are anywhere between 392 million and 844 million.

"All we can do," said one expert in this pleasant central Javanese city, "is prepare for the worst." This means resource-straining efforts in food production, housing, water supply, pollution-control, education and health care, to name just a few of the more obvious areas.

The United States, which has poured $42.6 million into Indonesia's family-planning efforts - more than in any program of its type in the world - has a deep vested interest in seeing positive results.

The greatest effort must be made in Java, according to Dr. Masri Singarimbun, director of the Population Institute at Jogjakarta's Gajah Mada University. Java, the fifth-largest of Indonesia's 3,000 islands, holds 70 per cent of the present population, 132 million.

That gives it a population of 2,700 people per square mile. By comparison, North Carolina, whose land area is almost the same as Java's, had a total population of a little moer than 5 million in 1970 - or 104 people per square mile.

By the end of this century, according to Research Minister Sumitro Djojohadikusumo, Java will be an "island city," with no elbow room and little area devoted to farming. This will mean that crops to feed the population will have to be grown on what are referred to as the "outer islands."

But the catch here is that few of these islands have fertile soil. Much of the potential farmland is carpeted by a think, spongy layer of weed-like vegetation that chokes off food crops.

This basic problem has been a major hindrance to the goverment's efforts at "transmigration," moving people from Java to the "outer islands"? to set up farming. Although lists of applications from Javanese eager for space outstrip the government's ability to move them, many transmigrants face harsh conditions when they get to their new homes.

But of more Australian anthropologist at the Population Institute, is the fact that neither family planning nor transmigration has effectively eaten into Java's population growth.

No more than 50,000 people have been moved from Java in any year since the government got serious about transmigration in 1951. Family planning has a spotty record on the island, with a high of 30 per cent of eligible married couples practicing birth control in East Java and a low of 12 per cent in the national capital, Jakarta.

Meanwhile, Java's population grows by 2 million a year.

This booming growth rate, according to Guinness' boss, Masri, is more the result of improved health conditions than a failure to practice family planning. Nationwide, Masri said, the annual birth rate is 3.8 per cent while the death rate is 1.7 per cent. This gives Indonesia an annual growth of 2.1 per cent.

By comparison, the crude birth rate in United States is 1.5 per cent while the death rate is 0.9 per cent, which works out to 0.6 per cent growth.

Despite this gloomy outlook. Masri and other experts are not particularly pessimistic. "It's to a question of optimism or pessimism," Masri said in a retwice our present population by the end of this century. And - if all goes well in family planning - we'll have a minimum of 392 million by the middle of the 21st Century." By that time, Indonesia will achieve zero population growth again, "if all goes well."

If all goes less than well, Masri conceded, Indonesia's population could reach nearly 900 million, by the middle of the next century - more than the current population of China.

Thomas Reese, deputy chief of the U.S. AID mission's family planning program in Jakarta, is more upbeat. Reese pointed out that early data show that Java's crude birthrate dropped between 17 and 20 per cent in the last seven years. By contrast, he added, India has been able to reduce its birthrate just 14 per cent in 15 years.

Indonesia's record is unprecedented anywhere outside China," Reese said.

Reese puts his faith in a program that has proven highly successful in Bali, the vacation island just off the eastern tip of Java. Under the plan, Village women form groups whose chief purpose is to discuss family planning and distribute birth-control devices.

here are now 25,000 of these groups in Bali and Java and, Reese said, this figure should double in the next two years. The group approach developed when family planning specialists found that women were failing to respond to a less-convenient approach that required them to travel several miles to clinics to discuss their problems and gather the next month's pills.

Under the group plan, certain women's homes are designated "depots" where pills and other devices are distributed. This idea has captured an element of prestige, Reese said, and many women are now vying to have the depots moved to their home.

The groups are also expanding their purposes from just family planning to such things as setting up housewives' cooperatives. Reese gave the example of one group that borrowed the equivalent of $60 from a bank to establish a chicken-breeding co-operative.

Masri and Guinness believe that the group approach has some application in Java, but they noted that Javanese are less integrated than the Balinese.

Where the two agree with Reese is in their conviction that the government is serious about family planning. New, small-denomination coins have been minted showing a couple and two children. This is in keeping with the fledgling ZPG movement, which preaches "Mary late and stop at two."

So, far, the average family on Java does not stop until it has four children. A four-child family was the original symbol of Indonesia's family planning program.

"So you can see," Masri said with a smile, "we have been making some progress."