If I run a 12/2 mc cable to feed three switches,one room has two 32 watt flouresent bulbs, the other two rooms have seven hi-hats in each room,each bulb at 65 watts.Can I run a14/2 mc cable for the switch leg , they will be on a 20 amp. ckt.
No you can not, it would be a clear violation of the NEC which in all common circumstances requires at least #12 on a 20 amp circuit.
I do not believe that it would be dangerous since the load is well within the capacity of #14, and in some countries it would be allowed. But under the NEC, no way.
Either use at least #12 or use #14 on a 15 amp circuit.