Type cannot be determined due to high level of neuroticism.
I think it changes substantially over time. At this particular point in time I would say America is...
E - Because its out there making a lot of noise with its wars and whatnot
S - Because its still polarized from 9-11 and only interested in the here and now
T - Because it isn't showing a tremendous amount of empathy for the rest of the world.
J - Because it has elected rather authoritarian leaders.
ESTJs thrive on order and continuity. Being extraverted, their focus involves organization of people, which translates into supervision. While ENTJs enjoy organizing and mobilizing people according to their own theories and tactically based agendas, ESTJs are content to enforce "the rules," often dictated by tradition or handed down from a higher authority.
If that doesn't sound like Evangelical-Christian, Conservative ruled America, then I don't know what does.
America seems to be getting more and more secular though.
LIBERAL MEDIA SLANDER!
I think you are right, and, considering the other two points you made about church attendance, the "traditional/stereotypical" God-fearing American population is probably dwindling, at least. Tons of people are Christians in different styles too, like the faith =\= church thing.
Still using a needle to break apart a grain of sand.
I think the type really has changed over time too.
1776-1790s = INTJ (Stong libertarian ideals, individualism, and desire to build something new that works)
1860s = ESTP (north) vs. ENTJ (south)
1920s = ENTP (roaring twenties, a time of great inovation and experiementation)
1930s = INFP (great depression, a time of great sadness and idealization about the future)
1940s = ISTJ (isolationist country stirred into a war machine)
1950s = ESTJ (ruled by strong, conservative forces)
1960s = ENFP (Love and peace baby)
1970s = ENFJ (women's movement and recession)
1980s = INTP (apathetic nation with focus on education)
1990s = ENTP (roaring 90's and the Clinton fiasco)
pre 9-11 GWB years = ESFJ
post 9-11 = ESTJ