After years of trying, Google has finally cracked the TV ad sales biz, cutting a deal with NBC Universal to broker spot sales for some of the Peacock’s cablers.

Multi-year deal calls for Google to handle some advertising sales for Sci Fi Channel, Oxygen, MSNBC, CNBC, Sleuth and Chiller cablers. Google has long sought to recruit major TV nets as partners in a service that would make Google a middleman broker of ad spots, auctioning inventory directly to advertisers through what it calls its “self-service” Web-based platform, Google TV Ads.

NBC U would not comment on the financial terms of the partnership, but it’s understood that Google will get a share of the revenue generated through Google TV Ads sales. The deal calls for NBC U to study the possibility of using Google TV Ads at its O&Os, and possibly expand its use to its top-tier outlets, NBC, USA Network and Bravo.

The Google TV Ads service has been pitched as efficient 24/7 means to selling spots, but major media has been wary of letting Google that far into the tent of the traditional TV biz — given the competish that Google and its Internet ilk have become in the global advertising marketing in general.

Media buyers, a key constituency for broadcasters and ad-supported cablers, have also been wary of Google TV Ads and its potential to cut into their role as in facilitating ad purchases.

Pact was announced Monday by NBC U sales and marketing prexy Mike Pilot and Tim Armstrong, Google’s prexy of advertising and commerce, North America. Partnership also calls for Google and NBC U to study new methods of testing advertising effectiveness and audience measurement, among other issues.