The difference is quite a bit. Here are Gallup's current poll results:
There is a fairly consistent trend: "registered voters" are to the left of "likely voters." Thus, the less interest one has in politics, as evidenced by not voting even though registered, the more likely that that person is to have liberal opinions.
This large difference is also one reason by polls are unreliable as a predictor of election outcomes. It is difficult enough for pollsters to reach a large and representative sample of adults and get them to answer the survey. The pollster also has to estimate (guess) how likely these respondents are to vote in an upcoming election.