The forum, scheduled for this week at the Lake Forest, Calif., megachurch, had been scheduled for two hours, with President Obama and presumptive Republican challenger Mitt Romney speaking with Warren for 50 minutes, the Orange County Register reported Thursday.
Warren hosted a similar forum in 2008 about this time between then Sens. Obama and John McCain, his GOP rival for the presidency.
"The  forum was praised for its unique format and fairness," Warren said Wednesday in announcing the decision against holding a similar forum this year.
Warren said he decided against this year's forum because the negative campaigning conflicts with the church's principles.
"We created the civil forums to promote civility and personal respect between people with major differences," Warren said. "The forums are meant to be a place where people of goodwill can seriously disagree on significant issues without being disagreeable or resorting to personal attack and name-calling."
"But that is not the climate of today's campaign," he said. "I've never seen more irresponsible personal attacks, mean-spirited slander, and flat-out dishonest attack ads, and I don't expect that tone to change before the election."