I know there have been a lot of surveys done over the years about these questions (at least polls of scientists in the United States - I'm not sure how much it's been done in other countries). As with all surveys, their methodologies are open to question so it's not always easy to say how reliable the results are. I am aware of at least one survey published in the scientific journal Nature in the 1990's which showed that around 60% of American scientists (astronomers and otherwise) either do not believe in or doubt the existence of God. This definitely represents a greater rate of disbelief and doubt than the U.S. population as a whole. Personally, I am often skeptical of the detailed results of these surveys, simply because I think a lot of people's answers to the questions depend on how the questions are asked. It's possible to believe in God but yet still have doubts, and sometimes surveys don't seem to do a very good job making this distinction.