Don't know if this is the easiest but the code is relatively short:
data example;
x='114wr01_ws02_2_3_MA_6_27_17';
call scan(x,4,pos,l,'_');
y = substr(x,1,pos);
drop pos l;
run;
I create a new variable with the SUBSTR function so you can check if the result is what you need.
call scan returns both the position and length of the of the nth, the 4 above, word delimited by characters in the last list.
Drop removes the temporary variables created by call scan after use.