Organized Christianity is a tremendous force for shaping opinion and conviction in society.  If the Roman Catholic Church and the Evangelical Protestant leadership were to make Peak Oil an issue the way Roscoe Bartlett has, millions would listen.  On a global level, the Pope has a world-wide bully-pulpit of perhaps unparalleled world-wide influence, owing to the prestige of Pope Benedict's predecessor.

Sadly, I think that the leadership, intelligentsia, and masses within organized Christianity will probably be the last people on the planet to catch onto what is really happening.  When Pope Benedict was elected this past April, I dubbed him the "Peak Oil Pope," because world peak will most likely occur during his pontificate.  And yet, I think there is a decent chance that he has not even heard of the notion.  The degree of oblivion among Christians of all persuasions is, unfortunately, of that sort of magnitude.

Personally I think religion will be a source of community in the coming crisis - a place where people can cooperate more instead of isolating themselves ever more. We have had End of Suburbia screenings at churches. I am doing one in December at a Unitarian Church on Staten Island.
And seeing as we're looking for a "prosperous way down" would one really want organized religion (which hasn't always been noted for its ethical and rational approach to the long view) to take action on something like this? I would prefer to see a groundswell of people from more liberal organizations take the reins, but then again, the church (catholic) is likely a better choice than the neo-cons. It seems like there's a lot of getting in bed with our enemy's enemy. While it may be necessary to raise awareness and prepare for a softer landing, I think skepticsm about ulterior/less-than-altruistic motives should be kept alive--I know I am sometimes afflicted with greed, malice and other base desires, how different can the papacy be?
You are touching on the deeper reason underlying the unsuitability of organized christianity to spread the word about Peak Oil.  Most of them (including the leaders and intellectuals) do not behave as Christians ought to.  In particular, they do not make a serious effort to find the truth and live according to it (Peak Oil being merely one example where this applies), and they do not seriously heed the Bible's stern warnings against the spiritual hazards of wealth and power.  These historically endemic realities go a long way towards explaining organized Christianity's failure with regard to Peak Oil.
As it happens, the article that just appeared today at the following link gives a very apt illustration of WHY wealth and power are so spiritually dangerous:

http://www.counterpunch.com/jensen10052005.html

That Christians would be the allegedly last people to figure out Peak Oil is not a failure of Christianity.  Most Christians spend more time, unfortunately, dealing with the secular world than with the world of faith.  They are thus necessarily affected by the milieu within with they live and operate.

Why do I argue that it is not the failure of Christianity? Well, take a look at the papal encyclicals of the last 150 years since the start of the industrial revolution.  The 'social doctrine' of the Catholic Church, as promulgated since the time of Leo XIII, has been about stewardship of creation, of not exploiting workers, of not pursuing wealth as an end in itself.  Now, it is the fault of the doctor when the patients fail to take their medicine properly?  Is it not, rather, greed operating to maximise oil output, profits, and to have the pursuit of never-ending growth, as encapsulated in our current economic theories?

The prima facie accusation of Catholicism being too worldly is ironic in that there are plenty of social theorists out there who argue that it is in fact too other-worldly, when they are trying to find an excuse for the relatively poorer economic performance of Catholic countries in Europe versus those of Protestant countries.

In any case, taking the lessons of history, the role of the Catholic Church would likely be the preservation of learning and knowledge once the industrial society that we live in now collapses.  Think of the role of the Catholic monks in writing the Bible and other books after the collapse of the complex civilisation of the Roman Empire.