JERUSALEM — Contrary to popular belief, the ultra-religious haredi population of Jerusalem is not growing faster than the rest of the city's Jewish population, according to a new Hebrew University study.

Projected figures for the year 2020 say the relative percentages of the city's Jewish sectors — consisting roughly of haredim, traditionalists and secularists — is expected to remain the same as it is now, while the percentage of Jews in the city's population will drop relative to the percentage of Arabs.

According to a study conducted for the city by Professor Sergio DellaPergola, chairman of the Harmon Institute of Contemporary Jewry of the Hebrew University, Arabs will make up 38 percent to 40 percent of the city's population of Jerusalem by the year 2020, up from the present 29 percent.

To strengthen the Jewish presence, Prime Minister Benjamin Netanyahu has agreed in principle to an incentive package to help students, young couples, and new immigrants stay in the city, and to create more jobs, according to city spokesman Haggai Elias.

According to DellaPergola, currently the Jewish population is 30 percent haredi, 10 percent national religious/non-haredi, with the other 60 percent comprising fairly traditional to very secular. "In the year 2020 it will be basically the same, with some very minor variations. And this is contrary to the common perception of the public, that the haredim are taking over and will continue to do so. This [perception] is not supported by this project."

One reason, his data showed, is the high number of haredi residents moving out of the city because of lack of affordable housing.

"In a sense, this is a compensatory factor for the higher birth rate of this part of the Jerusalem population," said DellaPergola.

The Arab population, on the other hand, which has an even higher birth rate than the haredim, tends to stay in Jerusalem regardless of housing conditions. There is also what he called the "phenomenon of Arab migration to Jerusalem."

DellaPergola said that his projections are based on the assumption that trends over the last few years will continue, "which includes the birth rate, death rate, internal migration within Israel and international migration to Israel," assumptions which are "not to be taken for granted."