The 29-year-old goalkeeper has decided to end his two-year self-imposed international exile and is in contention for the FIFA World Cup qualifiers against San Marino and Montenegro later this month.
England coach Roy Hodgson was in the stands as Foster produced a fine display to limit Chelsea to a 1-0 win over West Brom on Saturday and, after the game, Clarke praised his shot-stopper.
"For sure, Ben is international class," Clarke told reporters.
"He has already represented his country and proved that in the past.
"Now he is available for selection again, I'm sure he will prove that in the future.
"Ben is top class, has been great for us all season, is available for England and I'm sure that gives Roy a nice problem."
Foster has been in fine form for his club this term, but Clarke would not be drawn on comparing his goalkeeper with the incumbent England number one Joe Hart.
"It is all subjective," Clarke said.
"Ben has been great for us, his recent performances have been outstanding.
"I don't see Joe Hart week in and week out. (It's not) For me to judge, it doesn't really matter what I think.
"What matters to me is Ben is my number one keeper and has been in great form recently."
A chronic back condition contributed to Foster's decision to retire, but Clarke reckons the former Manchester United keeper is over his injury problems.
"The problems he had two years ago are gone by and large. They are clear," he said.
"He's worked hard this year and diligently away from the games as well, doing extra training and has got himself in a great shape."