"Marty's the quiet type." This is his pal's explanation for Marty's more subdued impact on TV fans who have watched him and partner George Maharis soar to fame on CBS's Route 66. The Milner boy's uneventful, happy home life, too, may have something to do with it. Married to former singer-actress Judy Jones, and dad of Amy, two-and-a-half, and Molly, born last January, Marty refuses to be separated from his family by long location trips, and all four Milners go traveling when the script calls for it. So far they've explored motels and hotels in places like Kanab, Utah; Port Hueneme, California; Merlin, Oregon; and Page, Arizona "with more coming up." Marty recently said: "Nothing is going to separate my family. It is the most precious possession I have and nobody will ever take it away from me." Marty and Judy had tried it the other way earlier: Marty on location, Judy and the kids at home. "And then one day Judy tearfully told me she had heard little Amy tell a neighbor's child that she had no father. That did it!" Judy now says of their constant traveling: "We'll admit that it has its disadvantages, but nothing has ever brought us closer together. We're growing together more each day." A pal feels that the reason for Marty's comparative emotional stability is the fact that he has been an actor since childhood, knows and understands the pressures of show business. And Marty himself has said: "Sure, stardom is swell, but so much depends on luck and timing, things like that. Love and marriage don't depend on luck. Those you have to earn, but once earned, they're yours for life!" As far back as 1947, Marty played one of the Day boys in Warner's Life with Father with Bill Powell and Irene Dunne, did 40 episodes of the early Stu Erwin TV series, Trouble with Father. Later he graduated to leading man status in pix like Marjorie Morningstar and Private Lives of Adam and Eve. How do he and his more mercurial, footloose buddy George Maharis get on, off the set of Route 66? "Just fine," he says. "We enjoy our partnership no end."