Can you defrost beef in frig. and then put it back in the freezer if you decide not to use it? ?

In actuality it is not the fear of cross contamination that you should be concerned about it is actually the fact that you are greatly increasing the growth of bacteria if you start freezing, defrosting, and refreezing the beef. Sure you can let it sit the the refrigerator for a few days while you defrost it but it is not wise to put it back in the freezer if you decide not to use it. Your best bet is to cook it and keep it in the refrigerator. In all safeness, it is best to just pull the beef out of the freezer when you are actually ready for it and you know you are going to use it.