Television advertising next year in the United States will see ad revenues grow 7.1 percent, due in large part to 2012 political advertising and the Summer Olympics, according to a forecast from MagnaGlobal released Oct. 11.

The updated forecast, MagnaGlobal’s “U.S. Media Owners Advertising Revenue Forecast,” continues to estimate ad growth across all major media this year of 1.6 percent or $173 billion in ad revenue for the year.

However, due to persistent weakness in the U.S. economy, MagnaGlobal has revised its overall 2012 growth forecast down from 4.8 percent to 2.9 percent, including political and Olympic advertising. Next year, MagnaGlobal expects ad revenues in the United States to reach $178.5 billion, significantly lower than the pre-recession level of $206.1 billion attained in 2007.

Television advertising revenue next year is forecasted to be second only in growth to online advertising, which is expected to see an increase of 11.6 percent, MagnaGlobal said.

Television will see an incremental increase next year of $3.1 billion with $2.5 billion in political advertising and $633 million from the London Olympics — up 5.5 percent compared to the Beijing games. MagnaGlobal added that most of the spending on political TV ads will benefit local stations.

Other local advertising media won’t fare as well, however. Overall, the MagnaGlobal forecast sees a decline of 1.1 percent in 2011 and 0.4 percent next year. The decline will be driven by weakness in newspaper ad spending, off 5.5 percent; radio, flat at -.04 percent; and a decline in outdoor of 4.5 percent next year.