Foster feels he is now ready to mount his own push for a place in Roy Hodgson's squad following a recent lengthy spell on the sidelines.
But the 30-year-old acknowledges Manchester City goalkeeper Hart is England's best at present and deserves to be first choice.
Foster, out for four months with a foot injury before returning just before Christmas, said: "It's taken me a while to get fully fit.
"It does take time to get your sharpness back, and I feel it's back now."
Assessing the England scene and with Hart back in form after being dropped by City boss Manuel Pellegrini earlier this season, Foster told Albion's official website: "You've got to look at Joe.
"He's come back into the Man City team and he looks as fresh as a daisy.
"He is a huge asset for the England team, and one of the best keepers I've ever trained with.
"I think he should start in the World Cup. As long as he keeps his performances up high then he will be a huge benefit for us in Brazil.
"Don't get me wrong, I want to play, but I've got to be realistic."
Before the World Cup, though, Foster faces a battle with his Albion team-mates to remain in the Barclays Premier League.
West Brom are one point and two places above the bottom three, and Foster said: "We're in a dogfight and we have to concentrate on ourselves.
"There are a lot of people (who) say to me from the outside we are too good to get relegated. But that doesn't mean anything really, does it?
"They say over 38 games that if you are relegated then you deserve to be.
"We've got to get on with it ourselves and make sure that doesn't happen. It's all in our hands, we have to crack on."