I work for a bible college who have asked all their salaried employees to work for half pay for 2 months because of a budget crisis is that legal

Yes, they may ask.

And unless there is a contract, they may also cut your pay anytime they want. There is a national min salary to be on salary. (without having to pay overtime) but yes, asking employees to take pay cuts ( often not temp ones) is very normal the last few years.

If they are just reqesting, you can say no of course. If they are forcing it, they may as long as they do not go under state or fed min.