Aiming to put its search product in front of more Web users, Yahoo on Tuesday said it had signed a multi-year partnership with Viacom that would place its search on 33 sites initially, possibly expanding to 140 additional sites worldwide at a later date.

In addition, the deal includes an agreement to use "Panama," a contextual ad service now under development at Yahoo. The moves show a willingness by the Sunnyvale, Calif. based company to compete with Microsoft and especially Google on all fronts.

Google has made many deals to place its search engine on other pages, including one with popular social networking site MySpace. Its contextual ad service is one of the most popular on the Web today.

Microsoft has made similar moves, but to a lesser extent. It has placed increasing focus on its adCenter advertising service, although that program currently only places ads on sites owned and operated by the Redmond company.

Some of the first destinations to use Yahoo ad and search technology would be Viacom's most popular sites, including MTV.com, VH1.com, Nickelodeon.com, comedycentral.com and BET.com. Depending on its success, the deal could eventually extend worldwide.

"Aligning Viacom's popular brands, leading content and large audience with Yahoo!'s more targeted, relevant advertising, marks the beginning of a powerful and engaging partnership between our two companies," Yahoo chairman and CEO Terry Semel said.

The agreement potentially carries a huge payoff for Yahoo. Viacom's combined traffic numbers among its entertainment sites are #1 in that category, and 11th overall. Over 90 million unique visitors were counted for Viacom's Web properties in February, according to data from comScore Media Metrix.