NEW YORK — Screenwriter Steven de Souza, whose movies have a combined gross in excess of $1 billion, has signed with the William Morris Agency, where he’ll be represented by Rob Carlson, Alan Gasmer, Gary Loder and Mike Simpson.De Souza, whose screen credits include “48 HRS.,” “Commando,” “The Running Man,” “Die Hard” and “Die Hard 2,” will follow up the directing debut he made on “Street Fighter” with “Flashpoint,” a political action thriller set in D.C., for Mike Medavoy’s Phoenix Pictures. While not as seismic as Arnold Schwarzenegger’s split earlier this week from ICM after a 15-year run with agent Lou Pitt, de Souza ends a 20-year run with agent Jim Berkus, most recently at UTA. While de Souza hailed Berkus for helping him become one of Hollywood’s premier action scribes, he made the move because he wants to become more than a writer. “I followed Jim and his Rolodex for years, but with the business getting global and based on content, content, content, I find myself staring at posters of 15 films I’ve written which grossed over $1 billion, and yet all the profit statements say, ‘We’re still in the red but we’ll be making another sequel,’ ” said de Souza. “I felt that the global reach of Morris would provide me with a more entrepreneurial approach to the things I’m doing.” He expected Morris to also set up numerous scripts he’s written that didn’t get made, the rights to which have reverted back to him. De Souza started in TV before getting his big feature break rewriting “48 HRS.” when the cast changed from Robert Mitchum and Clint Eastwood to Nick Nolte and Eddie Murphy. He’s turned back to that medium to create several series he’ll have a piece of. That includes “Descent,” a two-hour NBC pilot to shoot this summer, plus a series version of “Judge Dredd” and a series adaptation of the Robert Heinlein novel “Space Cadet,” the latter two produced by Ed Pressman.