The decline of fertility rates and the problems this may cause.
In 1967 the government embarked on a project to bring down the fertility rate of Indonesians, especially on Java and Bali, to what were considered more manageable levels. The program (see Two Is Enough: Family Planning in Indonesia Under the New Order, 1968-1998) has been a remarkable success, although exactly how much can be attributed to official efforts and how much to "natural" factors, is questionable, and the fertility rate has fallen from around 5.6 births per woman in 1967 to, probably, 2.2 today, a sharp, speedy drop.
From glut to shortage?
Currently there is a renewed campaign to increase the use of contraception among the people and presumably further depress the fertility level. The vice president has also spoken of a one child policy for Java as being ideal.
Total Fertility Rate (TFR)
TFR is the measure of the average number of babies born to women during their reproductive years. A rate of 2.1 is replacement level, where a population maintains its numbers, assuming no immigration or emigration occurs. When TFR is higher than 2.1 a population will grow in size and when it is less than 2.1 a population will decrease, although the fall in population will take some years to begin.
A 2005 report by researchers at the Institute of Southeast Asian Studies in Singapore breaks down the TFR of Indonesians by some of the major ethnic groups and by religious adherence. 
Period 2005-2010, low-high range for TFR.
Fertility in central and eastern Java, the areas with the highest concentration of the Javanese and Madurese, is already at below replacement level.
Into the future - 2025-2030.
Some urban legends about Madurese may need to be revised.
By 2050, or even earlier, fertility rates of all the major ethnic groups are likely to have fallen below replacement level, with the lower range estimates for the Javanese and Madurese being at the very serious, dire end of low fertility.
Or looking at TFR by religion, for 2005-2010:
"Others", Hindus and Buddhists, are already at sub-replacement level.
Projected for the period 2025-2030:
Projected for the period 2045-2050:
By 2050 the TFR's of all the religious groups are in retreat, but the weakness is greatest among Hindus and Buddhists, then Muslims, then Christians, assuming the lower ranges. The proportion of the latter two groups in the national population will rise, approaching a 90/10 split, or possibly closer to 85/15.
Net Reproduction Rate (NRR)
Another barometer of the situation is the Net Reproduction Rate. NRR is a measurement of the average number of daughters that each woman has. An NRR of 1.0 means each group of women has one daughter, on average, thereby replacing themselves and keeping the population steady. 
Period 2005-2010, NRR average range:
The Javanese and Madurese are already in negative territory on the daughter front.
Projected ranges for 2045-2050, low/high:
None of the groups, except perhaps the Bataks, is forecast to produce enough daughters to replace the then current generation of women.
About to go forth and multiply.
Fertility planners generally aim for a fertility rate of 2.1 but experience has shown throughout the world that decline in fertility rarely stops there, but continues down, in the most extreme cases to below 1.5, thus putting the long term survival of a people, and their language, culture, and religion, at risk. There is as yet no known case in the world where a people's fertility level fell below 1.5 and then "recovered" again to replacement level, for largely mathematical reasons - because the pool of people of reproductive age has already fallen too low. Those that are left would have to make rather "heroic" efforts to raise the rate by having quite large families.
The part of Indonesia with the greatest long term problem is Bali, because fertility rates there are at the lowest end of the current figures (1.9, 1996-1999) , and because the Balinese population, at around 3.5 million, is small to start with, and so it cannot withstand a sustained drop in TFR for long. If the predictions are correct, and no trends are bucked, it is likely that some time in the 22nd century non-Hindus, i.e., mainly Muslims, will form a majority of the populace of Bali, and the island's peculiar characteristics and culture will be of interest mainly to tourists, but to few of its inhabitants.
A museum piece.
Considerable population decline also creates some serious economic problems. When TFR drops below 2.1, gradually, the proportion of people aged over 65 grows, and the proportion of younger, working age people, falls. This can put great strains on governments and economies. The available work force, and hence tax base, shrinks, while the costs of caring for all the extra numbers of elderly rises, and in Indonesia, what's more, the raw numbers of elderly will be colossal.
Advanced economies, such as those in Europe, with well developed health and welfare systems, can generally manage this, although at massive cost, and with questionable long-term viability, but for poorer countries such as Indonesia the problems can be acute. Traditionally children here are expected to take care of their elders and thus take up the considerable slack in terms of government provision of services for the old, sick, and indigent. However as Indonesians become more westernised and materialistic, and given the tendency of children who grow up in small, one or two child families, to become individualist, possibly even selfish, it may be that Indonesians will become much less willing to shoulder the burdens that their old folk place upon them.
The figures for the aged as a proportion of the total population, 2005:
And the average projections for 2050:
The Javanese will be an ageing group (with elderly proportion larger than 10%) by 2025, the Madurese and Sundanese by 2030, the others by 2040.
It is hard to imagine today the problem which is approaching, given that Java is widely considered to be overcrowded, and given the perception that its people are still industrious procreators - however they are not any longer, above all in places like Yogyakarta and Jakarta. Many might welcome a decline in population for the island, but unfortunately such declines do not happen evenly across all age groups in proportion, they push up the number of old people and reduce the number of younger, productive ones.
One in four Javanese.
It is questionable whether many Indonesian leaders have thought about these matters, but they had likely better start soon. The Singaporean researchers posit the date of around 2035 as the time when the country will start to feel the effects of declining fertility and the consequent aging of the population. It may be around this time when the policy makers change their tune, and the beginnings of an Indonesian pro-natalist policy are formed, as has been the case in many European countries, where women are practically bribed to have babies. Any attempt at a pro-natalist policy will have to take into account the reasons people choose to have few, or no, children, and therein lies the most interesting question.
The percentage of Islam people in Indonesian has always been higher for political and national stability reasons. Good.
It reminds me of what I discovered about 10 years ago. All the people I met add themselves a few centimeters when I asked them how tall they were. Many were taller than I in theory but in reality I was taller (I am only 170 cm). Strange, so I try to find out why they always thought (and still think) they were taller than they really are.
What I discovered is they think they are taller because they are told they are taller. And why medical authorities, doctors, schools told them they are taller? Because they got instruction to do so. At Soeharto days, it seems it was a shame that Indonesian people were the smallest in Asia (and in the world if I believe what I read once in the Musee de l’homme in Paris). So the Departemen kesehatan received intructions. Adding a few centimeters won’t hurt nobody, it’s even good for the egos and it will make international statistic better. They must have done the same for economics stats.
Well, as we all know reality and facts are not what matters in Indonesia. Measurement stats, Religion stats, who cares if they are right or not? Yang penting Bapak senang!
I think we should be thinking of increasing the “quality” of the people not the “quantity” of the people.
Fertility rate is one thing that can affect population, but immigration policy also takes part in the population growth, some countries actually relies more to the immigration policy than fertility rate. But again I think the government should be concentrating more on the “quality” not the “quantity”.
Declining birthrates are somewhat representative of a higher standard of living enjoyed by most Indonesians today compared with 1967. People are quite possibly getting married later and putting off having that first child in the hope of saving up a bit of money before they have that child. Future imbalances in population can always be offset by immigration – this is what is happening in the west now. Most of the population growth in western countries is attributable to immigration. Speaking of immigration does any know what kind of immigration policy Indonesia has or for that matter the number and ethnicity of today’s immigrants to Indonesia?
I think the immigration policy consists of this two questions:
1. Do you want to become Indonesian citizen, explain WHY? Are you insane, there are a lot of people who want to get out.
2. Do you want to leave Indonesia for good? How much can you afford to bribe the Indonesian officials.
I agree many wany to get out but does Indonesia have a permanent residency policy, as Australia has ,whereas you can live in Aussie as a permanent resident and retain your own country,s passport.