England have thrived in white-ball cricket over the last two years, rising to the top of the one-day rankings while also being a force in the Twenty20 format.
But their Test form has slumped, losing the winter's Ashes 4-0 and suffering a 1-0 defeat in New Zealand before being held to a draw against Pakistan in home conditions.
Pietersen said: "I don't know which direction they want to go in. We won a T20 World Cup, we won the Ashes home and away, we beat India in India a few years ago.
"England haven't won a 50-over World Cup, I know that was the message a few years ago to do that and you can see they are driving towards that World Cup in England next summer, at the detriment of Test cricket and I think it's sad and frustrating for us as players who have played over 100 Test matches.
"The public care a lot more about Test match cricket than they do about the shorter form of the game.
"The big series will continue to exist, the Ashes will be fine, India v Pakistan, Australia against South Africa, all the real big series will exist."
England can continue their domination of the 50-over game in a forthcoming series with Australia, which follows a one-off game with Scotland.
Australia are in action for the first time since their tour of South Africa, where they hit the headlines for a ball-tampering scandal which saw captain Steve Smith, vice-captain David Warner and batsman Cameron Bancroft suspended.
They are sure to come under fire from English crowds, but Pietersen says the best way to repair their reputation is to win games.
"They have just got to win, when you win the media go with you, when they lose they hammer you," he added.
"Australia are always the pantomime villain, no doubt the English are going to go after them, but that's the nature of the beast, they always go after us when we go there."
