Updated

American voters remain divided on same-sex marriage, according to a Fox News national poll released Thursday.

The new poll shows that 49 percent of voters favor legalizing gay marriage, while 46 percent oppose it.  That represents a significant shift since the question was first asked on a Fox poll in 2003.  At that time, 32 percent said gays should be allowed to marry legally, and 58 percent were opposed.

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Support for gay marriage has increased by 27 percentage points among moderates since 2003, 22 points among independents and 21 points among Democrats.  Over the same time period, the number of liberals backing gay marriage more than doubled.

There are smaller yet still significant changes among Republicans (+10 points) and conservatives (+13 points).

And while support among voters under age 35 was fairly robust in 2003, it is also up by 9 points:  from 53 percent to 62 percent in the new poll.

Those most likely to favor legalizing gay marriage include those who never attend church (76 percent), liberals (72 percent), voters ages 30 and younger (65 percent), and Democrats (65 percent).  Groups most likely to oppose it include “very” conservatives (82 percent), Tea Partiers (75 percent), white evangelical Christians (70 percent) and Republicans (64 percent).

As the U.S. Supreme Court prepares to hear two same-sex marriage cases next week, the poll suggests a disconnect between public opinion and legal reasoning.

When asked the narrower question of whether gay marriage is a right guaranteed by the U.S. Constitution, 53 percent of voters say it is, while 43 percent disagree.

The same number -- 53 percent -- thinks each state should be permitted to decide whether or not to allow gay marriage in their state.

“Not surprisingly, many voters simply do not approach the issue the way a constitutional lawyer would,” says Fox News Legal Analyst Lis Wiehl. “Gay marriage is not just a divisive moral issue; it’s a thorny legal problem, too.  That's why the Supreme Court arguments on the Defense of Marriage Act and California’s Proposition 8 will be so closely watched.”

For example, 30 percent of voters who say a state should be permitted to ban same-sex marriage also say the Constitution guarantees that right.

In addition, eight percent of those who favor legalizing gay marriage do not believe it is a right guaranteed by the Constitution -- no issue there.  However, 14 percent of those who oppose doing so say gays do have a Constitutional right to wed.

Thirty-seven states have banned same-sex marriage by state statue and or constitutional amendment.  Where do people expect things to stand 20 years from now?  Nearly three-quarters think gay couples will be able to marry in all or most states.

Thirty-two percent expect same-sex couples will be able to marry in every state -- up from 26 percent who felt that way last year (May 2012).

Even among those opposed to gay marriage, 59 percent think all or most states will allow it 20 years from now.

Finally, gay marriage supporters are more accepting of those who disagree with them on the issue than are opponents.  Over three-quarters of supporters say those who oppose it have a right to that position and it should be tolerated.  Just over half of gay marriage opponents feel that way about supporters.

The Fox News poll is based on landline and cell phone interviews with 1,002 randomly chosen registered voters nationwide and was conducted under the joint direction of Anderson Robbins Research (D) and Shaw & Company Research (R) from March 17 to March 19.  The full poll has a margin of sampling error of plus or minus three percentage points.