With tens of thousands of U.S. nuns over age 70, the Roman Catholic Church is facing a massive financial shortfall for the care of retirees in religious orders - a gap that over the long term dwarfs costs from the clergy abuse crisis.

Though billions of dollars have been salted away, there still remains an unfunded future liability of $8.7 billion for current nuns, priests and brothers in religious orders. The financial hole is projected by a consulting firm to exceed $20 billion by 2023.

A June survey by the church's National Religious Retirement Office, not yet released to the public, puts spending for retiree care at $926 million last year alone. That compares with a total of $499 million received over the last 18 years from annual special parish collections to aid retirees.

The retirement realities far overshadow the burden from well-publicized sexual abuse cases, which have cost the American church more than $1 billion since 1950, with tens of millions of dollars in pending claims.

In some ways, religious orders face the same problem as many governments: increasing numbers of older retirees need benefits, but there are fewer workers to support them. America's younger workers pay now for the Social Security benefits of seniors, while younger religious support their older generations by caring for them.

Sisters, who make up 82 percent of retirees, are especially vulnerable.

Between 1965 and 2005, their numbers plummeted from 179,954 to 68,634, according to the Center for Applied Research in the Apostolate at Georgetown University.

With far fewer younger novices being recruited, the majority of sisters are now more than 70 years old, the retirement office's new survey said. Even though sisters usually work until age 75, caring for the retired population is a huge task.

The problem is discussed in the new book "Double Crossed: Uncovering the Catholic Church's Betrayal of American Nuns" (Doubleday) by former New York Times religion editor Kenneth Briggs. The book's main theme is that church authorities vetoed sisters' hopes for dramatic changes that would provide more freedom and effective ministries in the aftermath of the Second Vatican Council.

When Briggs completed his research, the annual care cost was running at $800 million and aid collections then totaled $480 million. He reports that the annual collections generate more than twice the receipts from the next largest special appeal, showing the regard parishioners have for the sisters and other retirees.

Briggs writes that the looming financial threat "sapped the creative energies of communities." But Sister Andree Fries, the 64-year-old executive director of the U.S. retirement office, disagrees.

She says "the impact is more minimal than one might think" because members of orders "are very much about mission" and not worrying about their future needs. Also, orders are "spending their future retirement money for current bills" so they are not uncomfortable at the moment.

What about the projected multi-billion-dollar gap? "Is it a big number? Yes," Fries said. "Am I discouraged that we'll ever get there? I'm sobered, but not discouraged, because religious are can-do people."

Some religious orders are financially healthy, but Fries' office reckons that only 4 percent of current sisters are adequately funded for their retirement needs. Typically, the problem is worst in smaller orders.

Religious orders are totally independent from dioceses in administration and finance. But they often serve in schools and other parish or diocesan institutions, so bishops and parishioners naturally feel a responsibility to help.

The religious orders' plight first gained national attention with a 1985 Wall Street Journal article by John Fialka. Contacted by fellow Catholics who offered donations, Fialka helped organize SOAR (Support Our Aging Religious), which pioneered in fundraising and last year received $1.4 million to aid retirees.

The U.S. bishops then followed suit, sponsoring their first annual collection in 1988 under the new retirement office, co-sponsored with three organizations of women's and men's orders.

The annual December collection was scheduled to cease next year, but at their June meeting the bishops agreed to extend the program another 10 years. Also, the retirement office plans to increase training for orders on how to manage investments, buildings and other assets.

Hundreds of orders have been forced to sell off assets to cover expenses.