For Warner Bros., Facebook has become a friend — and ally.

With plans to rent more movies via the social-networking site and nearing a deal to pony up around $90 million for movie ratings and recommendations website Flixster, Warners is making an aggressive push to take back control of its homevideo biz. Should the strategy work, it could provide the ammo that rival studios and independents are looking for to build out their own in-house online rental operations.

Warners has added “Harry Potter and the Sorcerer’s Stone,” “Harry Potter and the Chamber of Secrets,” “Inception,” “Life as We Know It” and “Yogi Bear” to the roster of films it streams via Facebook for $3. Offerings join “The Dark Knight,” which bowed on Facebook earlier this month and has tallied some 100,000 users for its app.

Warner Bros. has seen increasing efforts by the likes of rental firms such as Netflix and Redbox — and plans by Amazon and Google’s YouTube, among a growing list of others — to dominate the streaming market for movies and cash in on consumer demand for films on all digital platforms. With its plan to go straight to film fans on Facebook, WB is bypassing third-party retailers and digitally releasing pics on its own.

Through Facebook’s Credits currency (which users can opt into via credit cards, PayPal or gift cards), distribs don’t have to develop their own payment systems.

After a month out with “The Dark Knight,” Facebook has clearly given WB the results it’s been looking for and the studio now wants to reach out beyond fanboys to a broader family and female demo.

Although WB hasn’t officially released figures, nearly 100,000 people have used “The Dark Knight” app, according to Facebook’s Open Graph protocol, repping just 1.6% of the film’s 6 million fans that “like” the Batman actioner.

While that may seem low, consider that those views are for a film whose Blu-ray release was way back Dec. 2008. At the same time, the film’s “Dark Knight” page has added around 10,000 to 17,000 new fans a day throughout March, according to Inside Facebook’s PageData tracking service.

Films play via an app created with Milyoni, with Facebook taking 30% of each rental. Pics are available for 48 hours after purchase.

Other studios wouldn’t have to use WB’s streaming app; they could create their own and start renting through Facebook’s open platform.

WB’s move takes a page from ticket sellers like Ticketmaster, LiveNation, Eventbrite and TicketFly that have already turned to Facebook to sell more events to fans and their friends. The companies have found that adding a “buy” tab has helped boost sales among individuals who share events with friends.

TicketMaster and LiveNation, for example, have added a “friends” module through which users can see events their friends are attending. As a result, Ticketmaster found that, on average, when a customer on its site posts an event on Facebook, it generates more than $5.30 of direct ticket sales. When a customer “likes” or “recommends” an event, it generates an average of $3 in sales.

Ticketmaster research also found that 60% of fans would attend more events if they knew about them; according to Ticketmaster, 50% of tickets went unsold in 2010.

Turning to Facebook could prove a savvy move on Hollywood’s part.

Facebook attracts 600 million visitors each month, and as more marketers turn to attract consumers to their Facebook pages, those same companies are looking for ways to not only offer fans content on a regular basis but monetize that audience.

In the past, studios have struggled with how to keep their official movie websites relevant after a film is released on DVD.

Of course, it helps that the films WB has chosen to experiment with on Facebook are also some of the more popular pics and active pages on the site, attracting Batman, Harry Potter and Katherine Heigl fans.

“We’re pleased to expand our test with a variety of titles that will appeal to a broad audience,” said Thomas Gewecke, president of Warner Bros. digital distribution. “These titles have substantial followings on Facebook. The fan pages for ‘Harry Potter’ and ‘Inception’ alone are two of the most popular and active communities on the site.”

WB’s Facebook experiment could eventually transition over to those sites with the integration of a “watch” tab, as well, boosting homevideo sales.

The pickup of Flixster would further help promote Warner Bros.’ Facebook offerings by adding a rental button on a film’s page on the ratings site. Flixster boasts 20 million registered users, and the studio clearly sees the purchase as a way to boost its online rental biz.

Flixster owns review aggregator Rotten Tomatoes. The studio has acknowledged a potential conflict of interest and said it will create safeguards to make sure the company remains independently run.

Yahoo had previously expressed interest in adding Flixster to its collection of movie sites. News Corp. controls 20% of Flixster.

Facebook rentals by the numbers

$3: Value of 30 Facebook Credits, which can be exchanged for a WB movie rental for 48 hours

100,000: People who have used “The Dark Knight” app this month

1.6: Percent of 6 million fans who “like” Batman actioner and accessed rental app

10,000-17,000: New fans added to “Dark Knight” Facebook page each day through March

Source: Inside Facebook’s PageData, Facebook