Under a nonpersonal services contract direct supervision of contract employees is permitted Under a personal services contract it is prohibited?

The other way around. Per the Federal Acquistion Regulations:

"Nonpersonal services contract" means a contract under
which the personnel rendering the services are not subject,
either by the contract's terms or by the manner of its administration, to the supervision and control usually prevailing in relationships between the Government and its employees.

"Service contract" means a contract that directly engages
the time and effort of a contractor whose primary purpose is
to perform an identifiable task rather than to furnish an end
item of supply. A service contract may be either a nonpersonal or personal contract. It can also cover services performed by either professional or nonprofessional personnel whether on an individual or organizational basis. Some of the areas in which service contracts are found include the following:
(1) Maintenance, overhaul, repair, servicing, rehabilitation,
salvage, modernization, or modification of supplies, systems,
or equipment.
(2) Routine recurring maintenance of real property.
(3) Housekeeping and base services.
(4) Advisory and assistance services.
(5) Operation of Government-owned equipment, real
property, and systems.
(6) Communications services.
(7) Architect-Engineering (see Subpart 36.6).
(8) Transportation and related services (see Part 47).
(9) Research and development (see Part 35).