That’s one of the key findings of the 2005 Greater Boston Jewish Community Study, commissioned by the Combined Jewish Philanthropies, the central planning and fundraising arm of Boston’s Jewish community, and carried out by Brandeis University’s Steinhardt Social Research Institute.

Researchers interviewed 400 Jewish households by phone and an additional 1,400 individuals from a list provided by Jewish organizations. The margin of error differed by question.

Some local Jewish leaders say a key factor is the community’s heavy investment in outreach programming — $321,000 this year, almost 1.5 percent of the Combined Jewish Philanthropies’ $27 million campaign.

Those funds are given to programs aimed at interfaith families and individuals considering conversion run by the Jewish Community Center, Jewish Family Services, the Reform and Conservative movements and other agencies.

“There’s no other way to explain it,” said Ed Case, publisher and president of InterfaithFamily.com, a Boston-area nonprofit that encourages intermarried families to make Jewish choices.

The study’s preliminary findings, announced Friday, show strong growth of the Jewish community, which now stands at 265,500, or nine percent of the total population. That figure includes 57,000 non-Jews living in Jewish households; indeed, the study found that half of area Jewish households involve an intermarriage.

The number of non-Jewish adults in Jewish households has risen from 25,000 to 42,500 since 1995, the study found.

As increasing numbers of those interfaith families identify with the Jewish community, more and more are raising their children Jewish. Institute director Leonard Saxe, the primary investigator on the study, called the 60 percent figure “exceptional.”

In comparison, the National Jewish Population Study 2000-2001 reported that between 33 percent and 39 percent of children in interfaith households were being raised as Jews. The 2002 Jewish Community Study of New York put the figure at 30 percent in the New York area.

“When we first saw the 60 percent number, we said, ‘that can’t be true,’ ” said Gil Preuss, vice president for strategy and planning at Combined Jewish Philanthropies. But it made sense when he considered other figures: Some 37 percent of local intermarried families are members of synagogues, and more than 70 percent of the children who are being raised Jewish in intermarried families are receiving formal Jewish education.

The Boston study also reveals that 90 percent of local Jews “are connected in some way, even if it’s just giving money” to Jewish organizations, Preuss continued.

All of this suggests a Jewish community that is vibrant and growing, in contrast to previous surveys that showed a drop-off in Jewish populations in the Northeast.

Saxe and Combined Jewish Philanthropies officials are loathe to draw direct links between increased Jewish affiliation among the intermarried and increased communal investment in outreach programming, but Preuss said, “We hope it had some impact. Clearly we’ve tried to make the Jewish community and the CJP warm and welcoming.”

Other Jewish leaders are less hesitant.

“CJP is the only federation that has made a serious commitment for over 10 years to fund this,” said Paula Brody, outreach director of the Northeast Council of the Union for Reform Judaism, whose organization receives $140,000 a year from the Combined Jewish Philanthropies for a wide variety of adult-education seminars and workshops aimed at interfaith couples and individuals considering conversion. “We offered these programs before the CJP funding, but it has enabled us to expand our offerings and advertise them in the secular press, so we can reach the unaffiliated.”

Case says Boston’s outreach investment rate is almost 10 times the national average given by Jewish federations, a figure the United Jewish Communities is unable to confirm.

“Boston has the most highly organized and best-funded outreach of any community, with San Francisco a close second,” he said.

Preuss says the Combined Jewish Philanthropies used a 1995 Jewish communal study to redraw its strategic plan to encourage local synagogues and Jewish agencies to be more open and welcoming to the unaffiliated, particularly the intermarried. They increased funding for adult Jewish education, mainly run through synagogues, from $3.6 million to $6.4 million.

“It’s an activist approach” to building Jewish identity, “connecting people in diverse ways to Jewish life,” Preuss said. “That’s how we see our purpose, not just to collect and distribute money.”

Brody says her Reform outreach programs reach 600 to 750 non-Jews or interfaith couples every year, a number she compares to “a medium-sized congregation of unaffiliated people stepping into the Jewish community every year for the past 10 years.”

One such couple is Nick and Amy O’Donnell. He’s Catholic, she’s Jewish, and four years ago, even before their engagement, they took part in “Yours, Mine and Ours,” a Reform outreach program for interfaith couples.

The program “offered a place where we could work through the things that were important to us in an environment that wasn’t trying to herd us in one direction or the other,” said Nick, 31, noting that they were getting enough pressure from their families. By the end of the course, they’d decided to raise their children as Jews.

“Boston has sent a particular message of welcome, and the data shows that families are responding,” Brody continued. “If you put resources in this area, you will get results. You will get affiliation.”

San Francisco’s Jewish federation experienced similar results, according to planning director Karen Bluestone. That federation was one of the first in the nation to fund interfaith programming, she notes, following a 1986 Jewish communal study that revealed large numbers of intermarried families.

In the 20 years since, the Jewish population has more than doubled in the San Francisco Bay Area and intermarriage has increased, but increasing numbers of those interfaith households are identifying with the Jewish community.

A 2004 communal study showed that 40 percent of the children in interfaith households are receiving formal Jewish education, and 40 percent of the adults indicated that their interest in Judaism has increased in the past five years. The numbers are about the same for Jews and non-Jews, she said.

While Bluestone admits that “there’s no causality in the data,” she said she sees a correlation between increased outreach and increased Jewish identification.

“Due to the investments we’ve made since 1986 in outreach and training to be more welcoming to interfaith families, we’ve seen a rise in the number of interfaith families identifying as Jews and raising their children Jewishly,” Bluestone said.

Saxe says his study in Boston could “change the debate about intermarriage.” He noted gender differences: The children are raised Jewish in virtually every intermarriage where the woman is Jewish, but the figure is much lower when the Jewish partner is the man.

That suggests that Boston’s Jewish community should focus both on providing better Jewish education to non-Jewish mothers and on finding more effective ways to engage Jewish boys and young men in Jewish life, so they don’t “run from the bimah” after their Bar Mitzvahs, he said.

The findings also suggest that intermarriage, instead of having a negative effect on a given Jewish population, can lead to the reverse if more intermarried families affiliate with the Jewish community.

That’s true in Boston, Brody noted, where most of the “Jewish population” increase since 1995 is made up of intermarried households.

“What’s remarkable is that these families see themselves not as where the Jewish partner has married out, but where the Christian partner has married in,” she said.

Barry Shrage, president of Combined Jewish Philanthropies, says he hopes other Jewish federations will take their cue from Boston and San Francisco.

“Other communities are beginning to invest in outreach,” he said — “perhaps not to the level we have, but people are beginning to understand that it’s something that needs to be done.”