Test strategy defines required test approach for the 
project,it is company level terms.

Tst plan intructs u what to test ,who test ,when testing to 
stop,what techniques follow to design test cases.which 
contains complete informations abut automation tool.

Test Strategy is a high level document that contains the 
information about the test approach, organisations mission. 
All the information are completely at the organisational 
level.

Test plan is a detailed document that contains the details 
of the product such as what to test, when to test, how to 
test etc. Test plan can single for the whole project or it 
can also be written for every test level(component 
testing/itegration testing/system testing) etc.

Test Strategy is high level doccument contains test 
efforts,Test Configurational items,which tool emplyed,entry 
and exit cretaria for testing etc.Done by Test Manager

Test plan is concern to that project only contain Objective 
of testing,Assumptions,Risk Analysis,Test Tools,Scope,Test 
Scedule,Roles n Responssiblities etc.

So that both r important becoz Test strategy represents How 
Testing activities take place n Test plan represents How to 
perform testing,By Whom,How,When to start ?