The ABC/Washington Post survey released Wednesday also looked at attitudes on creating a path to citizenship for young illegal immigrants. The generational divide there was less stark.
The country is split on all three issues.
Just over half, 51 percent, of those polled support gay marriage and 47 percent oppose it. But 66 percent of adults under 30 are sympathetic to gay marriage, while only 31 percent of those 65 or older are. About half of those between 30 and 64 support gay marriage.
Only 48 percent of those surveyed supported legalizing marijuana, and 50 percent opposed it. On that issue, 55 percent under 30, 51 percent of those 30 to 49 and 52 percent of those 50 to 64 favor legalization, which drops to 30 percent for older respondents. That suggests the big divide is between those who came of age in the late 1960s and previous generations.
More than half, 57 percent, of the total sample support a path to citizenship and only 39 percent opposed it. Almost seven out of 10, 69 percent, of those under 30 approve, just about half of those in the middle brackets and 47 percent of those 65 and older.
The poll found women are more supportive of gay marriage by a whopping 18 percentage points, and men by 7 points of legal marijuana. Blacks were split on both issues, while 65 percent of Hispanics oppose legalizing marijuana.
All three issues came up in state referendums last week. Voters in Maine, Maryland and Washington state approved legalizing gay marriage, and Colorado and Washington legal recreational marijuana. In Maryland, voters passed a state version of the "Dream Act," giving some illegal immigrants in-state tuition at state colleges and universities.
The poll was conducted Nov. 7-11 with 1,023 adults contacted by telephone. The margin of error is 3.5 percentage points.