Forty-three percent of Democratic respondents said they preferred the New York senator and former first lady over other Democratic candidates in the 2008 contest, up from 39 percent in June, the poll showed.
That put Clinton even farther ahead of chief rival Obama, the Illinois senator who slipped from 25 percent in the June poll to 22 percent in July. Clinton and Obama have sparred in recent weeks, trading accusations last week over foreign policy positions.
The poll surveyed 1,005 adults from Friday to Sunday and had a margin of error of 3.1 percentage points.
Those polled cited Clinton's experience and competence highest among her positive attributes.