(UNDATED) In order to meet the challenges of a painful economic recession and sweeping demographic change, America’s religious communities will need to make significant changes.

Some Roman Catholic dioceses are already doing just that, merging or shuttering long-established parishes that are shrinking in membership. Those moves have caused resentment, including angry church sit-ins from irate parishioners who are (not surprisingly) deeply attached to their houses of worship.

As enrollment drops, underutilized Catholic schools are also being closed or consolidated. Immense seminary buildings — constructed decades ago when large numbers of men studied for the priesthood — are being sold or adapted for other uses. Because of the shortage of priests, aging Catholic clergy are stretched thin, often serving several parishes at a time. The retirement age for Boston priests was just extended to 75. All this is causing psychological and physical burn-out.

Membership decline continues apace within mainline Protestant churches; one Presbyterian pastor recently described his denomination as “older, grayer, and fewer in number.” This decades-long trend will force congregations to share ministers and other staff; ultimately, there will be a smaller number of congregations. Even evangelical churches, who were on a membership roll only a few years ago, are reporting stagnant growth. Recently two Baptist churches in Louisville, Ky. — one white, the other black — have united into one congregation.

Synagogues, too, face fiscal problems. The halcyon days of constructing or expanding Jewish houses of worship — call it the “edifice complex” — appear over. Congregational leaders are reassessing growth projections and seeking ways to contain costs.

If current trends continue, radical changes are required. But they need not be painful. Let’s start with an easy one.

Today, each church or synagogue maintains separate but limited collections of books, DVDs, religious periodicals, and tapes. It makes sense for neighboring congregations to pool their resources and create a central well-supplied religiously sponsored library for the entire community.

When I served as an Air Force chaplain in Japan and Korea, my Christian colleagues and I shared the same buildings for our offices and worship services. On Friday nights and Saturday mornings, the base chapel hosted Jewish Sabbath services; Catholic and Protestant services were held at staggered hours on Sundays. Provisions were made for Jewish and Christian holy days and daily worship.

There are similar arrangements in some American cities where a single building was constructed to house a synagogue and a church. Classroom usage is carefully scheduled, and there are many economic benefits in a shared facility: lower initial building costs, reduced utilities bills, shared security, insurance and savings on a host of other maintenance costs.

Another important benefit is the dynamic and fruitful interaction that takes place when clergy and lay people from different faith communities interact on a daily basis. America’s workplaces, political and educational systems are increasingly pluralistic in nature. Why not America’s houses of worship?

My experience has always been that Jews and Christians plumb deeper into their own faith commitments when they are in constant interaction with members of another religion. A shared synagogue/church experience must never produce a symbiosis, but rather a profound appreciation of one’s own and the “other’s” spiritual traditions.

When I served congregations in Missouri and Illinois, I remember when America was a land of expanding economic growth and land was easily available for new houses of worship; an era when each church, parish or synagogue was proudly located in its own unique building. It was understandable behavior and thoroughly human: “This is my house and that is your house!”

But such unbridled growth and go-it-aloneness may no longer be possible in today’s economically distressed America. Instead of pouring scarce funds into separate (and costly) sanctuaries, schools, and libraries, it is time for America’s religious communities to take seriously the words of the prophet Isaiah: “My house shall be called a house of prayer for all people.”

(Rabbi Rudin, the American Jewish Committee’s senior interreligious adviser, is the author of “The Baptizing of America: The Religious Right’s Plans for the Rest of Us.”)