In the survey, taken Thursday through Saturday, 47% of Clinton supporters say they are solidly behind Obama, and 23% say they support him but may change their minds before the election.
Thirty percent say they will vote for Republican John McCain, someone else or no one at all.
The findings spotlight the stakes for Clinton when she addresses the convention Tuesday and when her name is placed in nomination.
Say what you want about Barak, but he is no Clinton.
Clintons have experience in running campaigns at a national level and have had to deal with tough, experienced opponents. Obama, like Kerry before him, never has had to run a seriously contested race outside of their home districts.