I'd like to know the approximate percentages of claimed religious
beliefs in the United States.  Something like 70% Christian (30% of
those Catholic, 10%Babtist) 10% Jewish...etc.

Hello grngrl-ga,

Your question appealed to me because I recall seeing a breakdown
recently. Below are some sites (and descriptions) that will provide
the information you want. At the bottom I'll include the Google search
keywords and strategy I used to find these sites.

Adherents.com
Largest Religious Groups in America
<http://www.adherents.com/rel_USA.html>
--lots of stats here. They do include percentage breakdown by church

City University of New York
American Religious Identification Survey
<http://www.gc.cuny.edu/studies/key_findings.htm>
-scroll down below key findings. You will find a table (exhibit 1)
with an excellent breakdown. INcludes percentages.

The NES Guide to public opinion and electoral behavior
Religion of Respondent
<http://www.umich.edu/~nes/nesguide/toptable/tab1b_1c.htm>

Religious Tolerance.org
Religious Identification in the U.S.
<http://www.religioustolerance.org/chr_prac2.htm>

Infoplease.com
Largets 25 U.S. Churches
Numbers of members per church
<http://www.infoplease.com/ipa/A0001481.html>

Google Search Keywords:
-american religious preference percentage
-"u.s. churches" statistics
-"american religion statistics"
-u.s. demographics  "religion statistics" (limited by domain to edu
sites)

I hope this information satisifies your info needs. Please submit a
clarification request if you are uncertain about anything I've
provided here.

Thanks,

rapidreference-ga

Great research though it might have been nice to actually include one
of the listings in the answer.