Rita, My understanding, and from what I have observed in most social situations locally, is that it is most acceptable for a lady to ask a man to dance. From the practical side, most dances that I go to have far fewer men than women. If you are a single woman at a dance then you need to ask or you will be waiting a long time to get a dance in. This is the biggest complaint that I hear from ladies in our area. I have discussed this with other guys and we are very flattered by an invitation to dance. I never look at it as anything beyond a social dance and it is very good for leaders or followers to dance with new partners to hone their skills. I spoke to a lady who is taking lessons from a chain studio (AM) and her biggest fear right now is that she cannot dance with anyone except her instructor. I told her to get out to the local dances and ask as many men as possible to dance with her.
My contention is: if you learn the steps and practice on a regular basis then you should be able to dance with anyone else who is at the same level of instruction.
Please if you are out and there is an available man, ask him to dance, you won't regret it. -Jim