expressions - Phrase or way to say 'thought should be given'

To think about something or give it some thought is akin to pondering.

ponder:

think about (something) carefully, especially before making a
decision or reaching a conclusion.

Hence, you can look at the following alternatives:

1. consider as to how to decrease the deficit


2. ponder on how to decrease the deficit


3. study as to how to decrease the deficit