Cracks in foundation?

I'm looking at possibly buying a house, my first. It's an older place, built in 1946 and needs some fixing up (mainly siding and windows) which I would hire a contracter to do. I can buy the place cheap so I have enough breathing room to pay for fixing it up. The thing that has me concerned though is the basement walls. They are constructed of concrete cinder blocks, but in a few places on the outside the mortar between the blocks has cracked and there is a noticeable gap, at least 1/2" wide or more in spots....as if the foundation has settled over the years. Is this something to be overly concerned about? Can I just fill the cracks in with fresh mortar, or are more serious problems such as an unstable foundation lurking and what can be done if that's the case?