My potatoes have blight. Is it O.K. to put the tops in the compost?
don't think so, tomatoada, have a look in pests and diseases, I'm sure I read it somewhere :)
No don't compost haulms with blight. If possible burn them.
If you have a compost heap which gets reasonably hot and breaks down its constituent materials within a few weeks then it is perfectly safe to compost them. However, this usually requires a certain amount of finely shredded material (such as grass mowings or other shredded soft stuff) and if your heap, like most lottie heaps, stays cooler and takes longer then you should not compost them immediately. You could burn the stuff, or alteratively you can put it into a bin bag, tie the top, and leave it for a few weeks, during which time both green matter and blight spores will die - then you can compost it.
are you positive its blight?