He doesn't seem much younger, because he was still quite hunky on "Dallas," but it's definitely a different spin for Dack Rambo. Composed, learned gentleman in a silver suit. A tough military leader at the same time. He travels to Earth and enlists the aid of a special friend as he tracks down a notorious band of aliens he's been fighting elsewhere in space.
The show is "Wonder Woman," more specifically the December 1977 two-parter, "Mind Stealers from Outer Space." A decade or so before he landed in Dallas as long-lost Ewing cousin Jack, Rambo portrayed Andros, a highly evolved friend to our Amazon princess. Together they work to take down the alien threat, and at the end Andros even tries to woo Wonder Woman to more stellar aspirations.
See it for yourself at the WB, and catch the full BRBTV synopsis of this and other "Wonder Woman" episodes at the IMDb.