For three years, Charles S. Robb was out of the spotlight that had become so familiar, first as the son-in-law of President Lyndon Johnson and then as Democratic governor of this conservative state. But on Tuesday, the 49-year-old lawyer re-entered the national arena in decisive style, fashioning a huge victory over Republican long-shot Maurice Dawkins, a retired black minister and Washington lobbyist. Robb said today he won because ``we attempted to identify with mainstream values that are crucial to success at the national level,'' such as strong defense and fiscal responsibility. With 99 percent of the precincts counted, Robb had 1,448,389 votes or 71 percent, to Dawkins' 587,887 votes or 29 percent. The former Marine combat officer has built a career by making Democrats electable in conservative Virginia. Once known only as the former White House military social aide who married LBJ's daughter, Lynda Bird Johnson, he won the lieutenant governor's race in 1977 in his first bid for elective office. Four years later, he ran for governor in the first sweep by Democrats of the state's top three offices since 1965. Robb was a popular governor who was credited with overhauling the state bureaucracy and making major gains in education funding. He also opened positions of authority in state government to blacks and women and appointed Virginia's first black Supreme Court member. The former governor was also one of the architects of last spring's Super Tuesday presidential primary, intended in part to give the Southern vote collective strength. But Robb's tenure was shaken by prison troubles that drew national attention when six death row inmates escaped in May 1984. Robb, who could not succeed himself under Virginia's constitution, had been out of office for three years and practicing law until his bid for the Senate. ``I've been unemployed for a long time, and it looks like I just got a job,'' he said.