Atheist authors Richard Dawkins and Christopher Hitchens are currently having their time in the sun. Their books and live broadcast debates with Christians are very popular. These adherents of atheism enjoy calling believers in supernatural creation/design in our universe "irrational." Many believers in God and God's apparent actions are troubled when doubters wave the "irrational" banner, like cheerleaders at a pep rally, provoking applause from the audience. What's a believer to do?
A dictionary search connects rationality with reason. In turn, reason is defined as thinking in a connected, sensible, and logical manner. Belief in an omnipotent Creator (the CAUSE) more powerful than His creation (the EFFECT) should strike us as reasonable. Effects have causes. Design implies a designer. Both statements are logical. Belief in the existence of God who has acted to produce our universe from nothing is certainly not irrational.
In contrast, believers in God have reason to accuse atheists of being irrational when they ascribe the current order, constancy, and predictability of the universe to randomness and chance. Even the theistic evolutionary beliefs of some Christians who attribute evolutionary speciation to unknown or uncertain processes -- can those beliefs be said to be more rational than belief in supernatural creation? Atheists and agnostics claim there is no evidence of the existence of God. The evidence of the natural world, however, does not support their belief system, but rather, ours.