Using one login to access multiple pages(subdomains with different themes)

I have a news site with a login to add calender events, I also have a /classifieds theme with its own login. I want to link the two pages logins, so that you don’t have to login twice to gain full site functionality. http://www.bradleycountypulse.com
Thanks for any suggestions
JG

I have posted this in the How-to section twice with NO response. If I need to post elsewhere, please let me know.