Test stratagy and test plan both means that planing the 
testing activity. 
    But test stratagy is an organizational level term, 
whaich can be used for all the projects in the 
organization. 

    Test plan is a project level term which can be used 
only for that project.

Test Stretagy will be prepared by test manager.

and Test Plan will be preapred by test lead. Which involves 
test plan identifier, Description, scope, Approach, 
Features to be tested and not to be tested, Test schedules, 
deliverables, nature, resources used, staff & training, 
Entry & Exit criteria, Suspension & Resumption criteria, 
P/F criteria, etc..

In simple words test strategy means approach for 
testing.i.g Manual testing / Automation /Load testing...

Test plan is document describing test 
approach,objective,scope,schedule ,resources,functions to 
be tested,functions not to be tested &o will perform which 
task.

Ideally Test manager prepares test plan.