That entirely depends on the person, not the belief.
An atheist might value life because an atheist probably believes that once you kill something, that's it, nothing more, the end, they're just gone. And so, life should not be taken away because you've taken everything from that person. An atheist may believe that life is worthless, though, as there's no divine/metaphysical justification for it, so it's as meaningless as a random rock you may pick up off the ground.
A religious person may think life is valuable because God gave it to them and having been given by God it is sacred and not to be destroyed. Or, in the case of Buddah, because this is effectively the only life we have (in the next reincarnation we will not remember this one, so it doesn't much matter after we die). A religious person might think life worthless/of little worth because it's the afterlife that counts.
And then there's the whole question of the life of the individual versus life as an idea. Does an anti-abortionist oppose it because of the sanctity of life (i.e. on principle), or because they specifically have in mind the life of the unborn? Does an atheist value the individual human, or humanity?
It doesn't really have anything to do with religion/atheism. It's about the person. Religion/atheism do have a say, yes, but you'll probably find similar numbers (by proportion) on both sides.
