How can I send the same email letter to every elected government
official at the same time?

I don't believe you can. In order to prevent spam and other junk
email, some Representatives restrict emails to ones that come from
their websites (see http://www.house.gov/writerep/wyrfaqs.shtml#listrep
for the House policy), and similarly, if you look at
http://www.senate.gov/general/contact_information/senators_cfm.cfm on
the Senate website, you will see that some senators list the web form
for email.

(Of course, I could be wrong...)