Despite his comments that he thinks the matter should be left to the states, many gay rights advocates strongly believe that it must be dealt with nationally — and that Obama is quietly on their side. Conservative critics of the president suspect the same, citing this as one way the president might tack left if reelected.

And some Obama supporters who are uncomfortable with same-sex marriage fear that in a second term, he would come under enormous pressure to back efforts to impose the legalization of gay marriage from the federal level…

In particular, they are worried that the president’s preference for state-by-state recognition will give way to the view that same-sex marriage is a guaranteed right under the Constitution. That issue is at the heart of a case that could come before the Supreme Court in its term beginning in October: It involves Proposition 8, a voter-approved California constitutional amendment that bans gay marriage.

Obama opposed Proposition 8. But if the court accepts the case, it could ask the administration for its view on whether marriage is a fundamental right that cannot be withheld from same-sex couples. Such a finding could sweep away state decisions on gay marriage, as well as the bans in 30 state constitutions.