It 's pretty unusual for a pressure line to clog. The first thing that I would look for is a shut valve, barring that, I would suspect that the stoppage is in the faucet. Shut off the water and disassemble the faucet/tub valve. If you don't see anything obvious, have a helper slowly turn the pressure back on. If this doesn't find the problem then work back from the faucet till you do find it.
I forgot to mention another possible source, any time dissimilar metals are joined together, there can be a substantial build up of corrosion, i.e. brass or copper to steel or iron. Check all connections.
thanks for the info. will be trying to unclog tomorrow. I also think its the faucet