Not out of the box. Those permissions are per-folder.
You might want to see if the Policy Maker tool from http://www.autoprof.com
can do this, though. It adds a lot of capabilities to GPOs.

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Sue Mosher, Outlook MVP
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> Is it possible to use group policies to control sharing a calender,
> by default I want to turn on "REVIEWER" on for "DEFAULT" for everyone
> in the orgainzation. HOW CAN THIS BE DONE.