Two-third of young voters, part of President Obama's base in 2008, are ambivalent about voting in November, a poll released Thursday shows.

Fewer than three in ten (27 percent) of 18- to 29-year-olds surveyed by Harvard University's Institute of Politics say they will definitely turn out for the midterms, down from 31 percent in February and 36 percent last September.

The survey also found that among this demographic, lauded in 2008 for its enthusiasm, only 18 percent say they are politically engaged, down from 24 percent in November 2009. 

"In 2008, 'millennials' took control of their own destiny, entered the political process and changed the direction of the country," said John Della Volpe of the Institute of Politics (IOP). "Two years later, the challenges they face as a generation could not be higher. Let's hope they reverse the current decline in interest and participation."

The decline also mirrors a nine-point drop in millennials' approval for Obama since November (58 percent to 49 percent), though most do continue to lean left, preferring that Congress be controlled by Democrats and approving of current Democratic over Republican members by 11 points (39 percent to 28 percent).

Looking toward 2012, Obama emerges between 25 and 30 points ahead of potential Republican candidates Newt Gingrich, former Alaska Gov. Sarah Palin and former Massachusetts Gov. Mitt Romney.

In a matchup between Obama and a generic Republican, however, Obama only led by one point (31-30), with the plurality (39 percent) of young people saying they were undecided.

The IOP interim director John Culver noted these figures as an opportunity for candidates to engage with young people.

"Recent election cycles show candidates who can motivate this critical demographic will have an important advantage," he said.

The survey has a margin of error of 2.2 points and was carried out between Sept. 23 and Oct. 4 from 2,004 interviews.