Six of the 12 host stadia have failed to meet the December 31 deadline while delays have also affected work on hotels, airports and roads.
FiFA president Blatter pointed out that Brazil has had seven years since it was awarded the tournament - previous hosts only had six years or even less time.
Asked if World Cup hosts realised the scale of work involved, the FIFA president told Swiss newspaper 24 Heures: "No. Brazil has just found out what it means and has started work much too late.
"No country has been so far behind in preparations since I have been at FIFA even though it is the only host nation which has had so much time - seven years - in which to prepare."
Even South Africa, which is much less wealthy than Brazil and had to build all its 2010 venues from scratch, were more prepared.
Work on three stadia in Brazil is likely to go on until the middle of April, just a few weeks before the start of the tournament on June 12, but Blatter admitted early in December that there is "no plan B".
This includes the Itaquera Arena in Sao Paulo which will host the opening ceremony and match of the finals between Brazil and Croatia. It has suffered one problem after another, culminating in the death of two workers in November.
The Brazilian government announced it would be completed in February, only for - a day later - FIFA to confirm another deadline of April 15.
Blatter also conceded that he expected there to be more of the protests that dominated last summer's Confederations Cup.
He added: "I am an optimist not a pessimist. So I am not worried. But we do know there will be again be manifestations, protests. Those during the Confederations Cup - in this same country - were generated out of the social networks.
"There was no specific goal but during the World Cup the protests will perhaps be more concrete, more organised. But I also believe the football will be safe, I do not believe that Brazilians will attack the football directly. For them, it's a religion."
Blatter also dropped another hint that he may change his mind and stand again for the FIFA presidency in 2015.
He said: "I cannot answer with a yes or a no but simply state that I do not feel tired enough to say that I will not stand."