Which committee decides the speakers in a conference: SOC or LOC?
I would expect this to be done by the scientific organizing committee (if there is not a more formal peer review process).  It is a scientific task, after all, and requires some level of scientific judgment of the quality of the submission.

Agree with TheWanderer that the "local organizing committee" is typically responsible for purely logistical issues, and does not make decisions about what is included in the program.