One of the most important exceptions to the Federal Torts Claims Act is the so-called "discretionary function" exception. According to this exception, the Federal government is immune from liability for the damages caused by discretionary conduct of one of its employees. As you would imagine, of course, much of the litigation in this area revolves around the question of whether the particular conduct in question should be considered to be discretionary. As a general rule, courts have developed a two step analysis for dealing with the question: first the court must determine if the conduct is in fact discretionary, which is usually done by examining whether it was mandatory or whether there were options available for the actor. Second, it has to be determined if the discretionary conduct is the type of conduct for which the government should be given immunity, which usually requires the court to determine if the decision to engage in the conduct was based on public policy grounds.
However, different courts have interpreted, or applied, the analysis differently. The blog Circuit Splits (which is devoted to providing references to splits on issues among circuit courts) just published a summary of the split on this topic. If you are interested in this topic, you may want to take a look at it here.