To the alarm of some local Jewish leaders, a new survey indicates that the Philadelphia area's Jewish population is growing but aging, the under-18 group is shrinking, and those 40 and younger identify less with Jewish causes than do their elders.

In the city and four suburban Pennsylvania counties, the Jewish population has increased about 10 percent, to 214,700, since the Jewish Federation of Greater Philadelphia's last survey 13 years ago.

However, the number of Jews younger than 18 is down 16 percent.

Among those 62 and older, 12 percent of marriages are interfaith, compared with 45 percent among Jews younger than 40. Of the latter, just 29 percent raise their children in Judaism, according to the survey, released last week.

Unless such trends are reversed, said Ira M. Schwartz, the federation's chief executive, "there will be declining financial support for the Jewish elderly, for family services, for synagogues, and for Israel."

The report, he said, "has turned out to have far more serious implications than we anticipated when we commissioned it. This is a real wake-up call . . . but we don't know yet what we're going to do."

The survey of 1,217 Jewish households was conducted from March to June by the Einstein Center for Urban Health Policy and Research, a division of the Albert Einstein Healthcare Network. A household was counted as Jewish if at least one occupant identified as such.

About two-thirds of the households came from federation mailing lists, 30 percent from random phone calls, and 8 percent from calls to households with typically Jewish surnames. It did not include New Jersey or Delaware.

The results will be posted on the federation's Web site in about two weeks.

The increase in the Jewish population of Philadelphia, Montgomery, Bucks, Delaware, and Chester Counties was a "real surprise," Schwartz said. "Most of us had predicted it would go down.

He and others involved in the survey said it was not clear why the number of Jewish children younger than 18 had declined since 1996, from 41,000 to about 37,000. Only the Jewish communities in South Florida have a smaller percentage of youths.

The area's Jewish population is the seventh-largest in the nation. With the addition of about 45,000 Jews in Gloucester, Camden, and Burlington Counties, the Philadelphia metropolitan area ranks fifth, after New York; Los Angeles; West Palm Beach, Fla.; and Chicago. Comparisons are difficult, though, because some of those areas have not conducted Jewish population surveys in nearly a decade.

In Philadelphia and the four suburban counties, Reform Judaism accounts for 41 percent of the Jewish population, and is the largest and fastest-growing denomination. Fifty-three percent between ages 18 and 39 identify themselves as Reform.

While 30 percent of Jews in the survey identified as Conservative, only 18 percent of young adults did. Schwartz called the trend "alarming for Conservative Judaism," which has been losing members nationally as well.

Six percent of the survey group identified as Orthodox, but among young adults, the number was 9 percent. Reconstructionists accounted for about 3 percent across all age groups.

About 10 percent of respondents said they belonged to no denomination, and about 3 percent considered themselves "secular" or nonreligious.

Among other results:

In 73 percent of all married Jewish households, both partners are Jewish. In Chester County, that number drops to 40 percent.

Chester County has the highest proportion of Jewish households with children, 48 percent. Philadelphia has the lowest, 10 percent.

Twenty-two percent of all Jewish households earn more than $150,000, 14 percent earn less than $25,000, and 26 percent said they were "just managing to make ends meet."

Contact staff writer David O'Reilly at 215-854-5723 or doreilly@phillynews.com.