WASHINGTON — Television ads in this year's presidential race are more negative in tone than in any of the previous three White House campaigns, according to a report Wednesday by the Wesleyan Media Project.

Almost two-thirds of presidential ads on the air between June 1 and Sept. 30 were negative, compared to about 40 percent during that period in 2008. In 2004, 34 percent of the ads in that period were negative, while for 2000 the figure was 18 percent, the report said.

Fewer than 8 percent of presidential ads on the air between Sept. 9-30 were positive. Ads promoting President Barack Obama during that three-week period dropped from about 28 percent in 2008 to 2.5 percent this year. Ads promoting the Republican presidential candidate, Sen. John McCain in 2008 and former Massachusetts governor Mitt Romney this year, declined from 32 percent to 15 percent.