Mr Putin signed the Russian law after it had been approved by the Russian parliament.
He told officials he saw no reason not to sign it, and said he would sign a presidential decree to modify the support mechanisms for orphaned children.
There are lots of places in the world where living standards are higher than they are here, Mr Putin said.
Are we going to send all our children there? Perhaps we should move there ourselves?
Some 3,400 Russian children were adopted by foreign families in 2011, almost one-third of the children going to American homes.
Over the same period, the number of children adopted by Russian citizens was 7,416.
In the past two decades Americans have adopted more than 60,000 Russian children.
The Russian government's politically motivated decision will reduce adoption possibilities for children who are now under institutional care, US state department spokesman Patrick Ventrell said.
We are further concerned about statements that adoptions already underway may be stopped and hope that the Russian government would allow those children who have already met and bonded with their future parents to finish the necessary legal procedures so that they can join their families, he added.
