To put it simply: Clicks are not the same as Visits.
According to official Google explanation:
Google AdWords tracks clicks, while Google Analytics tracks visits. If a user clicks on your ad twice within thirty minutes without closing his or her browser, this is registered by Analytics as one visit to your site, even if the user left your site and then returned shortly after. For example, if a user clicks on your ad once, clicks the back button, and then clicks your ad again, AdWords registers two clicks while Analytics registers one visit.
However your numbers are off quite a bit. Have you review Analytics implementation -- are all the pages being tracked?