The 12th bishop of Pittsburgh, successor to Bishop Donald Wuerl, will inherit a diocese not terribly unlike many others in the United States, where 2,000-year-old religious traditions sometimes grind against contemporary mores, challenging religious leaders as they work to reconcile the two.

What Bishop Wuerl's successor faces is a church coming into thin years.

Sometime in the next decade, the number of active priests in the six-county Catholic Diocese of Pittsburgh will fall below the number of parishes -- 215 at last count. On a given Sunday only 36 percent of the adults who call themselves Roman Catholic attend Mass. A diocese that once had more than a million members and was the second most populous in the nation now numbers 800,000.

"We closed parishes that our Protestant brothers and sisters would have envied the size of and we did that primarily because we don't have the priests to staff them," said Nicholas Cafardi, dean emeritus of Duquesne University School of Law, a canon lawyer and longtime adviser to the diocese.

A shortage of priests is not unique to Pittsburgh. The diocese ordained one man this year and current projections suggest no more than two or three ordinations yearly for the next five years.

How the next bishop handles this problem is likely to be an important measure of success.

"The No. 1 priority is our envisioning ministry program," said the Rev. Ronald Lengwin, diocesan spokesman for the past two decades and a man who has observed the church's transition.

The "envisioning ministry" program seeks ways to share parish resources, with an emphasis on bringing women into a larger role as parish administrators, freeing priests to deliver the sacraments that are the core of the church's ministry.

How effective that effort can be is undetermined.

Just days before he received word he would become archbishop of Washington, D.C., an archdiocese with fewer Catholics than Pittsburgh but located in the center of political power for the Western world, Bishop Wuerl summoned an old aide to take over a new post.

The Rev. Frank Almade, a member of the bishop's inner circle of aides, was asked to assume the post of vicar of clergy for the diocese.

Along with the crisis in vocations, Father Almade worries, too, about keeping adult Catholics versed in the principles of their religion -- one currently arguing over points as fundamental as whether to ordain women or whether Christ married Mary Magdalene as told in the fiction work, "The Da Vinci Code."

"We need new vehicles of saying to our Catholics that formation in the faith is a lifelong thing," he said. "It's a fancy way of saying we need adult education. You have to be continually learning about your faith."

In the course of his earlier work for Bishop Wuerl, Father Almade said he saw a man grow into the job -- something the next man is likely to have to do as well.

"It wasn't just only top-down. It was a matter of listening to people on the ground."

Bishop Wuerl's top assistant, Auxiliary Bishop Paul J. Bradley, sees the falloff in Mass attendance, and the influence of "The Da Vinci Code," as hints of a church-wide problem in faith.

"Not unlike other parts of the church in the United States and other parts of the world, there's a growing number of nominal Catholics, fewer practicing Catholics," he said. "It's a reflection of where we are that a particular movie could affect a person's faith perspective."

Bishop Wuerl had one advantage not guaranteed to his successor, an advantage spoken clearly when, upon assuming office, he noted that no one had to give him directions to the cathedral in Oakland.

"Pittsburghers like Pittsburghers," said Dr. Cafardi. "It's not that we're chauvinists, but we tend to prefer Pittsburghers, and Bishop Wuerl was a Pittsburgher.

"He was one of us. He was born and raised here. He understood Pittsburgh.... I don't know what the Holy See will do, but I hope in their wisdom they will again give us one of our own as our bishop."

Whether such a suggestion reaches beyond the borders of Allegheny County is doubtful. Bishop Wuerl might be taking over the archdiocese in the capital of the world's most powerful democracy, but he is not doing so on behalf of one.

In Pittsburgh, as in every other diocese, Rome gives the final word. It could take months, not days, for Pope Benedict XVI to provide the name of the man who will inherit the diocese Bishop Wuerl ran and the challenges he leaves behind.