Do atheists ever engage in circular reasoning? They certainly do and they do it quite often.
One of the most common claims of the New Atheists is that science proves that all religions are wrong. Yet as the New Atheists agree, science is (currently) defined in such a way that it cannot support any religion or point to God. If any scientific theory does point to God, it is immediately dismissed as “pseudoscience.” So what many atheists are actually claiming is that a method, which can only support their worldview, proves that their worldview is correct. That certainly sounds like they are assuming what they are trying to prove which can also be described as a circular argument. It's similar to the way some Christians argue that they know God exists simply because they know the Bible is true.
To be sure, it is perfectly legitimate to consider scientific (i.e. empirical) evidence when evaluating religious truth claims. However, that evidence needs to be lifted out of the realm of science and considered within the realm of philosophy. It is only in philosophy that one can follow the evidence wherever it leads.
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