I took up Moshe Arens' suggestion, made on this page last month ("Demographic bogey" ), to take a look at the figures of the Central Bureau of Statistics that he finds so encouraging. And what do I find? For one, that the statistics bureau deals only with data within the Green Line, namely Israel, and data about the Jews of Judea and Samaria. As far as the Arabs in the territories are concerned, we will have to look elsewhere.

What is so encouraging about the figures for 2010? I found that within Israel, Jews constitute 75.5 percent of the population, but that the proportion in 1998 was 79.2 percent, and 81.7 percent in 1988. In other words, the percentage of Jews in the Israeli population is constantly declining, in spite of the influx of about 1 million immigrants over the past two decades.

According to the forecasts, in 2015 the percentage of Jews will decline to 73.5 percent, and will drop to 70.6 percent by 2025. Only in 2030 will there be, for the first time, a miniscule increase in the proportion of Jews, bringing us to 72 percent. What is there here to make Arens happy?

If to this harsh data we add foreign workers, immigrants from Africa, tourists who did not return to their homeland and Palestinians who enter the country and don't return home, then the percentage of Jews drops to 70 percent of the inhabitants of Israel. What's so wonderful here? It's an unpleasant picture.

But in recent months Arens has been preaching in favor of the annexation of Judea and Samaria to Israel (according to him, that is the way to prevent the existence of two states in this narrow space ). Of course, that poses a serious demographic problem. So what does Arens do? He receives data from some American team, which enables him to count how many Arabs live in Judea and Samaria, how many have left, how many are leaving and how many will leave the Land of Israel in the future. He also keeps tabs on the number of births and deaths and asserts "scientifically" that only 1.5 million people live in Judea and Samaria. If we erase 1 million Arabs from the board, then there is a Jewish majority in the Land of Israel; the redeemer has come to Zion and the demographic bogey is dead.

But I don't rely on American teams, and instead turn to the head of the Civil Administration in the Israel Defense Forces, who reports to me that there are presently about 2.6 million Palestinians living in Judea and Samaria, and in Gaza their number is estimated at 1.5 million. Anyone who doesn't rely on the IDF can access the figures of the Palestinian statistics bureau, whose last census was held in 2007, under the aegis of representatives of the Norwegian government; their numbers are similar to those of the IDF (after subtracting the residents of Jerusalem who were already counted by the Israeli statistics bureau ). In both cases it turns out that, not counting Gaza or foreign residents, Jews constitute 59 percent of the total population in the Land of Israel. If you do count Gaza and foreign residents, there are somewhat fewer Jews than there are Palestinian Arabs.

There is no choice but to deal with forecasts for the next decade or two, and it turns out that by then the proportion of Jews will have declined to 42 percent. That means an end to the Jewish entity in the Middle East. The demographic bogey, then, is alive and threatening after all, and we still haven't discussed the density of the population or the issues of internal security that we can expect from a hostile population of millions of people.

There is no choice but to tell Arens that the right-wing Betar ideology on which he was raised went bankrupt a long time ago and it won't help if he virtually erases 1.5 million Arabs from the territories. They are here. The conclusion is frighteningly simple: Whoever brings about the establishment of a single binational state in the Land of Israel will doom the Jews of Israel to destruction. We, the sane majority who still live here, will not allow anyone to do that.

The writer is a professor emeritus at the University of Haifa.