Halo: Combat Evolved Manual Description:
The Elites will undoubtedly be back as your most feared Covenant opponent. The Elites will be able to make cover, as well as destroy it. Once again, there will probably several "ranks" of Elites, defined by color. The feared Sword-Elites will also be present, as seen in the Halo 2 E3 demo. And don't forget about the invisible Elites, who are just waiting to club you in the back.
The Elites are back, smarter and faster than ever, so never let your guard down.