One can certainly be a libertarian and be pro-life (anti-abortion). Many, many are. I am one.
Here is an explanation of the reason that libertarians (and others) cannot agree on the laws concerning abortion;
Some libertarians believe that a baby yet unborn is not a person or human being. They call it a fetus sometimes and think that it is a group of cells without being an individual life. Just like a finger or toe or ear. They therefore believe that it can be disposed of without any legal or moral consequences.
On the other side are those who believe that an unborn is a person, starting from conception. Those people are the possessers of the right to life. Therefore abortion is murder.
That is the crux of the issue. Is it a human life or not? No one that I know can say with 100% certainity.
My position is that if there is any chance whatsoever that it even might be a life, then we must err on the side of defending human life particularly for those who cannot defend themselves.
One other aspect that almost all libertarians I know agree on is that the constitution gives the federal government no powers with concern to murder. It is reserved for the states. Therefore they believe that the decision should be overturned and the matter sent back to the states to be decided by each one of them. I also believe that and if it ever gets back here I will work to make it illegal again.
I hope this helps answer your question.
Actually its a little more complicated than that. The question is not whether it is a person or not. The question is whether it is an individual person or individual humanbeing. It might also be noted that it does not just end there. This is just the starting point for various libertarian theories on the topic (i.e. some Randian Libertarians assert a necessity to assert ones claim to life, some Christian libertarians reserve rights till after the first breath of life with entry of the spirit into its body, etc, etc, etc.).
My position is that if there is any chance whatsoever that it even might be a life...
My position is that if there is an chance it might suffer pain, then error on the side of not introducing pain.