New York City ? With control of Congress at stake, politicians are aggressively taking to the airwaves. Through mid-October, the number of television campaign commercials was up 31 percent compared with the same period four years ago, a report released Thursday found.

Nielsen Monitor-Plus counted 942,900 political ads running between August 1 and Oct. 15. That doesn’t even take into account the last week before the Nov. 7 election, when advertising is at its heaviest.

The biggest factor in the ad increase is the spending by national party organizations.

Together, the Republican and Democratic national committees paid for more than 110,000 TV ads through Oct. 15. During the same period four years ago, they ran less than 50,000 ads.

Democrats also are being more aggressive in their spending. The Republican National Committee placed 10,000 more ads four years ago than its Democratic counterpart; this year the GOP edge was 2,000.