Help with Where/Case/Having

I have a program that looks for all of the projects in the database. I need to make a change where if the project starts with the letters 'MER' I have to exclude all resources with a code of 'CA'. If the project doesn't start with 'MER' I don't want to exclude any resources.
Here's the current code:
Select
LOC_ABBR,
PROJECT_NM,
RESOURCE_NM,
From PROJECT_TIME_ADJUSTMENTS PTA,
PHH_RESOURCE PR
Where PTA.RESOURCE_CD = PR.RESOURCE_CD
And CUTOFF_YR = 2003
And CUTOFF_MO = 02

Order By LOC_ABBR, PROJECT_NM, RESOURCE_NM

What's the best way to do this? I've tried changing the where statement, using a CASE statement, and a HAVING statement, but can't get it to work.

Any suggestions?

Thanks in advance.

Hope this meet your requirement

Select
LOC_ABBR,
PROJECT_NM,
RESOURCE_NM,
From PROJECT_TIME_ADJUSTMENTS PTA,
PHH_RESOURCE PR
Where PTA.RESOURCE_CD = PR.RESOURCE_CD
And CUTOFF_YR = 2003
And CUTOFF_MO = 02
And PROJECT_NM Like 'MER%'
And RESOURCE_NM Not Like 'CAL%'
Union
Select
LOC_ABBR,
PROJECT_NM,
RESOURCE_NM,
From PROJECT_TIME_ADJUSTMENTS PTA,
PHH_RESOURCE PR
Where PTA.RESOURCE_CD = PR.RESOURCE_CD
And CUTOFF_YR = 2003
And CUTOFF_MO = 02
And PROJECT_NM Not Like 'MER%'