In his 2008 book, Render Unto Caesar, Archbishop Charles J. Chaput of Denver wrote, "Catholics who live so anonymously that no one knows their faith . . . aren't really living as 'Catholics' at all."

Now, six months since his installation as the Roman Catholic archbishop of Philadelphia, Chaput is about to publish a short e-book that, like Caesar, exhorts Americans of faith, especially Catholics, to save the nation from what he considers its downward spiral into secularism.

At just 19 pages, A Heart on Fire: Catholic Witness and the Next America would fill no more than a chapter in his previous book, and - at 99 cents - is priced accordingly. Its release date, online only, is Tuesday.

It touches on themes in Caesar and in many of Chaput's speeches and homilies. The religious faith that informed the nation's democratic principles, he argues, is on the wane, and to its peril.

Chaput begins with a swipe at the American news media, which, he says, can be "rigorously intolerant" of ideas outside their own secular worldview, and especially of religious values.

He then takes aim at "our national leadership in 2012" which, he says, seems "frankly hostile to religious engagement in public affairs."

Apparently completed in February, A Heart on Fire does not mention President Obama by name. But it does refer to his administration's recent mandate that religious institutions such as Catholic universities and hospitals must provide coverage of artificial birth control as part of their employees' health insurance plans.

In speeches, homilies, his weekly online column, and the pages of The Inquirer, Chaput has vigorously denounced the contraceptives policy as an assault on religious freedom because the Catholic Church condemns artificial birth control as sinful.

Yet, he writes in his e-book, "in government, the media, academia, in the business community and in the wider culture, many of our leaders no longer seem to regard religious faith as a healthy force."

This putative trend "marks a break with most of American history, and we're likely to see more of the same in the years ahead."

Citing the late American Jesuit John Courtney Murray, Chaput argues that the foundational belief in the "intrinsic dignity of human nature" at the heart of American democracy was rooted in the Christian worldview of the nation's founders.

"In effect, God suffused the whole constitutional enterprise," he says, but "the America emerging in the next several decades is likely to be much less friendly to Christian faith than anything in our past."

A quarter of American adults under 30 "now have no affiliation with any religion," he says, and many of those seem hostile to Christianity.

Two centuries ago, the French journalist Alexis de Tocqueville marveled at how "all noise ceases" on Sundays, whereas today, Chaput says, Americans have been justifiably described as "galley slaves of pleasure."

Anyone alarmed at the nation's moral decline can point to mass media or universities or "special interest groups," says Chaput, but the finger of blame must also curve back on the pointer. "We Christians - including we Catholics - helped shape it with our eagerness to fit in, our distractions and overconfidence, and our own lukewarm faith," he writes.

He concludes A Heart on Fire by arguing that Catholic universities and youth movements have the capacity and obligation to lead the next generation of Catholics to "see the beauty of the world in the light of eternity."

Contact David O'Reilly at 215-854-5723 or doreilly@phillynews.com.