The Frenchman believes an increase in the number of participants at football's showpiece event would be embraced by all concerned.
He says only three days would be added to the schedule and that the event would reach a wider global audience.
It is possible that Platini will soon be in a position to make such calls, with it expected that he will rival Sepp Blatter for the FIFA presidency in 2015.
Platini agrees with Blatter's recent call for more African representation on the World Cup stage, but feels a possible expansion could also benefit Asia, America and Europe.
He told The Times: "It's good for everybody.
"I totally agree with Mr Blatter that we need more African and Asian (countries). But instead of taking away some European, we have to go to 40 teams in the World Cup.
"We can add two African, two Asiatic, two American and one from Europe. I support this idea totally."
Platini believes the growth of FIFA in recent decades justifies a bigger World Cup.
"Football is changing and now we have 209 associations," he said.
"There are more countries so why reduce? Forty is not so bad.
"You have three days more of competition and you make more people happy."
I think that there shouldn't be too much read into this. It's the strongest hint yet that Platini will run for FIFA presidency, which is fantastic news when you consider the alternatives are Blatter (again) or the guy from the Caribbean. Platini, at the very least, is a football man rather than a bureaucrat. I think Blatter made the first move in an attempt to garner support from Africa, which makes up roughly 25% of FIFA members. Blatter can afford to annoy the UEFA nations, as they're almost certainly going to fall behind Platini anyway. Then Platini comes out with a retaliatory statement that should keep everyone happy. It's all just politics people...- ajsr1982