"Three in 10 Americans interpret the Bible literally, saying it is the actual word of God. That is similar to what Gallup has measured over the last two decades, but down from the 1970s and 1980s. A 49% plurality of Americans say the Bible is the inspired word of God but that it should not be taken literally, consistently the most common view in Gallup's nearly 40-year history of this question. Another 17% consider the Bible an ancient book of stories recorded by man."
Odd fluctuation in recent years.
Gallup.com, July 8, 2011
See the article for lots of other numbers on this issue.