Xbox Entertainment Studios is deep in negotiations with Showtime to develop a live-action “Halo” drama series that is a high priority for the Microsoft production unit headed by Nancy Tellem.

Xbox Studios has been developing a drama series spin on the vidgame franchise with Steven Spielberg’s Amblin TV banner for more than a year. It’s understood that the company is close to a deal with a pair of showrunners to steer the series adaptation of the expansive bible developed by screenwriter Stuart Beattie, but the deal is not envisioned as a straight-to-series pickup.

Xbox aims to develop “Halo” and other properties as high-end series productions in an effort to enhance the Xbox platform as an entertainment service for its base of 48 million subscribers.

The deal with Showtime has taken a long time to work out because the sides are charting new territory for a show designed to air on Showtime as well as Xbox, with enhanced interactivity built in for the latter platform. Details are still being hammered out, but sources say the plan is to have episodes bow on Showtime first, followed by the Xbox window.

Tellem talked up plans for “Halo” and a host of other shows earlier this week as part of Microsoft’s NewFront presentation but did not mention the Showtime component. The various companies involved have taken plenty of time to work out the deal because “Halo” is such a prized property for Microsoft.

Reps for Showtime and Xbox declined to comment. Spielberg is exec producing the TV adaptation along with Beattie, Amblin’s Justin Falvey and Darryl Frank. Xbox Entertainment Studios is producing with 343 Industries, which oversees all things “Halo” for Microsoft.