The Supreme Court agreed Friday to take up the explosive issue of same-sex marriage, thrusting itself into a policy debate that has divided federal and state governments and courts, as well as voters in nearly 40 states.

The high court’s long-awaited decisions to hear challenges to the federal Defense of Marriage Act and California’s Proposition 8 ban on same-sex marriage move the issue to the top of the national agenda following a year in which advocates scored major legal and political victories.