WASHINGTON — Americans are evenly split on whether the Supreme Court should rule that same-sex marriage must be legal nationwide, according to a new Associated Press-GfK poll.

The poll was conducted just before the Supreme Court heard oral arguments on Tuesday in a case that will likely decide whether state laws banning same-sex marriage are constitutional.

But the poll also finds that Americans are more likely to favor than oppose marriage for gay and lesbian couples being legal in their own states.

According to the new AP-GfK poll, nearly half of Americans favor laws allowing gay and lesbian couples to wed. Just over a third are opposed.

But Americans are split down the middle on what action the Supreme Court should take when it rules on the marriage case later this year, with 50 percent saying it should rule that same-sex marriage must be legal nationwide and 48 percent saying that it should not.

The poll shows a massive partisan divide on both questions. Two-thirds of Democrats and just under half of independents say they support legal same-sex marriage, compared to less than 3 in 10 Republicans.

Only 15 percent of conservative Republicans want same-sex marriages to be legal, while 46 percent of moderate Republicans say they are in favor.