As the Obama administration weighs its response to the legalization of the recreational use of marijuana in Washington and Colorado, a new YouGov poll has found that a slim majority of adults believe the federal government should not enforce federal laws — under which marijuana use is still illegal — in those states.

The YouGov survey, conducted for The Huffington Post on Dec. 5 and 6, found that 51 percent of the 1,000 adults interviewed said the federal government should “exempt adults who follow state law from enforcement.” Thirty percent said the federal government should “enforce its drug laws the same way it does in other states,” the poll found.

Support for legalizing marijuana use — and not simply for medical purposes — has been rising steadily since the early 1990s. The most recent polls have shown a public divided. A CBS News poll from mid-November found an even split, with 47 percent supporting legalization and 47 percent opposed. A more recent Quinnipiac University poll found a bare majority supporting legalization, 51 percent to 44 percent.

But the YouGov poll is one of the first to ask not whether marijuana use should be legal but what the federal government should do about it now that two states have legalized recreational marijuana use.

The share of respondents who want the federal government to leave the states alone roughly matches the share of respondents that polls have found favor legalization: about half.

The difference is in the percentage of adults who favor the federal government still enforcing federal law. While polls have found that half, or close to half, of American adults generally oppose legalization, the YouGov poll found that only about a third of respondents favored enforcing federal law in states that had decided to legalize use.

Instead, 20 percent of respondents in the YouGov poll said that they were not sure what the federal government should do, more than double the percentage of adults that polls have usually found to be undecided on the overall question of legalization.

The YouGov poll is just one data point, and more polling will yield a fuller picture. But a portion of American adults who oppose the legalization of marijuana may also be partial to states’ rights, and those two impulses are in tension here.

The CBS News survey pinpointed the same conflict. According to the poll, 59 percent of adults said the question of legalization should be left to the states, rather than the federal government, including 49 percent of respondents who oppose legalization.