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The most drastic social policies would probably be officially limiting families to one child each as in China. As a corollary to the 'limited family size' approach, I'd include killing unwanted baby girls but that's my opinion..
Less drastic measures would include family planning, education (sex education and traditional education which improve socioeconomic conditions) and women's empowerment movements. The latter have been shown to be particularly effective in the developing world.
That being said, most governments haven't done all that much to really limit population growth. As highlighted by the fact that we got our 7th billion person last year and at twenty six, I'm old enough to remember when the 6th billionth was born. Which is really frightening.
In my personal opinion, the most effective control on overpopulation in the U.S. implemented by the government is the disillusionment and lack of faith in the future of this country had by most thinking people of my age. No one can afford children at the moment and no one has enough faith in the future to have them, so economically limiting indirect factors are possibly a more significant "population control policy" in America than actual programs aimed at reducing birth rates.