The two players have both played for Saints first team and go straight into the Lions’ 17-man squad at Sheffield Eagles on Sunday
Prop Forster, 19, and back row Hale, 20, both made their first team debuts last season.
Swinton coach Steve McCormack said: “We are delighted with these two lads who are both in St Helens top 25 squad.
“We have a good relationship with Saints and last year we had Warren Thompson and he did really well for us.
“We have been a bit short of numbers and quality in our front row and these two have come at a really good time for us.
“Both are thought really highly of by St Helens coach Royce Simmons.
“Carl is a big front rower who has played for England and Scott has played quite a few times in Saints back row.
“They are just the type of players we are looking for and have been in a very good environment.
“They have a lot to prove because their aim is the get in the Saints first team on a regular basis. If they play well for us they will eventually do that.
“Both St Helens and ourselves are really happy with the arrangements.”
Swinton have a full squad to select from for Sunday’s game at Sheffield.
“We’ve got good competition for places and there are going to be some very good players missing out,” said McCormack.