Blatter also said that the vote would be held with only 22 voters if two members of the executive committee, suspended for allegedly offering to sell their votes, were not reinstated by then.
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A defiant Blatter added that the sport was in safe hands with FIFA, expressed confidence in the committee which is investigating the case internally and questioned the methods of the Sunday Times newspaper which made the allegations.
"We are five weeks from the final decision so there was never a question of changing anything in the procedure," he told a news conference after a two-day meeting of the executive committee.
"On December 2, here in Zurich, FIFA's executive committee will hold a vote, which will be a secret ballot, and will determine the national associations which will host the 2018 and 2022 World Cup."
"We cannot stop the match which has already started."
But Blatter reflected that it was probably a mistake to pick both hosts in the same vote.
"I have said I assume the responsibility and I think it was not the right way to go," he said. "But now, we are in the situation where we have to go on but I'm not convinced now it was the right decision."
Russia and England are bidding to host the 2018 World Cup along with joint bids from Spain/Portugal and Belgium/Netherlands. Japan, South Korea, Australia, United States and Qatar are candidates for 2022.
NO FEAR
FIFA has been shaken by allegations of vote-selling by two FIFA executive committee members and collusion by unnamed bidding nations.
Amos Adamu of Nigeria and Reynard Temarii of Tahiti have been provisionally suspended by the ethics committee, after being accused by the Sunday Times in Britain of offering to sell their votes to undercover reporters.
But Blatter said he had confidence in the ethics committee, which is investigating the case and is due to meet from November 15-17, to make a definitive decision.
"We have the necessary instruments inside FIFA," he said.
"If something dramatically serious happens before the end of November, then of course the results will be dramatic and we will be ready for that."
Only the 24 members of the executive committee can take part in the votes and there had been confusion as to what might happen if that number was reduced to 23 or 22.
But Blatter cleared up the question.
"If people are suspended for the vote on December 2, they will not be replaced," he said.
Blatter deflected other questions on the case, saying most people involved in the sport trusted FIF
