"You've got conservative whites here, and I think there are some whites who are probably not ready to vote for an African American candidate," Rendell told the editorial board of the Pittsburgh Post-Gazette in remarks that appeared in Tuesday's paper.
To buttress his point, Rendell cited his 2006 reelection campaign, in which he defeated Republican challenger Lynn Swann, the former Pittsburgh Steelers star, by a margin of 20 percentage points.
Rendell, chairman of the Democratic National Committee in 2000 and previously Philadelphia's mayor, endorsed Clinton on Jan. 23.
Pennsylvania holds its primary April 22.
Later Tuesday, Rendell's spokesman said the governor did not mean to offend anyone.