Buildings at Sir Thomas Picton and Tasker Milward schools are said to be in poor condition and there are worries over standards at Tasker Milward.
The council cabinet heard the number of spare places there was causing concern.
There are eight options, including closing Tasker Milward and transferring pupils to Sir Thomas Picton.
According to inspection body Estyn, Tasker Milward is in need of significant improvement and is categorised as causing concern with "unsatisfactory learner outcomes".
The school received a formal notice of improvement from Pembrokeshire council in November.
Sir Thomas Picton school was judged to be "good and outstanding".
A review of secondary education in the Haverfordwest area noted surplus places at Tasker Milward were running at 22% currently, but due to rise to 43% by 2018.
In contrast, Sir Thomas Picton had "acceptable" spare capacity but was forecast to be oversubscribed by 2018.
Tasker Milward currently has 869 pupils and Sir Thomas Picton 1,184.
The council is considering eight options, including:
A preliminary consultation on the future of secondary education in Haverfordwest will begin next month, with sessions on 11 and 13 March at Pembrokeshire Archive.
Two secondary schools in Haverfordwest could be merged or replaced with a new school after Pembrokeshire council agreed to consult on their future.