Only in Virginia, one of his campaign aides confides, would Chuck Robb be considered a Democrat.

He is for right-to-work laws, for amending the Voting Rights Act, he "supports conceptually much of what Ronald Reagan is doing." None of this would distinguish him from many Virginia Democrats, who habitually elect Republican presidents, governors and congressmen--or, for that matter, from his Republican rival for the governorship, J. Marshall Coleman, who is also a handsome, careful ex-Marine suffering from seemingly terminal ambition.

What makes it striking in Robb's case is that he is the son-in-law of the most liberal Democratic president of modern times, Lyndon B. Johnson. Although Robb owes his political career to the celebrity conferred on him by marriage to Lynda Bird Johnson, he obviously feels he owes the father of the Great Society no ideological allegiance.

And what makes it wonderful for him is that Republicans who couldn't stand LBJ see Robb as one of their own, and Democrats, except for those few crazy northern liberals, think of him as LBJ's heir.

The whole thing is a perfect illustration of "the Virginia way," which is to reproduce as far as possible the atmosphere of Brigadoon, where time stands still, and ambiguity, mist and fog prevail.

Robb is so cautious that when asked by the Richmond Times Dispatch about his favorite books, he ducked--"I have tended in recent years to read a lot of books." Coleman boldly came out and said his favorite was Stendhal's "The Red and the Black."

Lynda Robb complains that Coleman is trying to make it a contest between Ronald Reagan and LBJ. But since Robb is fleeing the shade of his formidable father-in-law, there seems little danger of a referendum on the Reagan Economic Recovery Program v. the Great Society. Chuck went about chucking traditional Democratic constituencies: the blacks by announcing his intention to revise LBJ's masterwork, the Voting Rights Act, and labor by endorsing Reagan's anti-union stance in the air controllers' strike.

But the latest polls, which have Robb 11 points ahead of Coleman, show blacks overwhelmingly in his corner. Any place else this might be surprising, but in 1977, when Coleman made a successful run for attorney general, his opponent, Edward J. Lane, a leader of Virginia's "massive resistance," won 77 percent of the black vote "because he was a Democrat."

Said a campaign aide, "Selma, Ala., is ahead of Virginia in race relations."

And race is still much on Virginia's mind, if the questions put to the two rivals at a debate staged before the Virginia Manufacturers Association at the Homestead, the posh Hot Springs equivalent of the "ole plantation," are representative.

One stern tycoon, who could not bring himself to mention the name of Martin Luther King, asked Coleman and Robb what they would do if presented with a bill making a holiday of the birthday of "someone who was neither patriotic nor law-abiding." Gov. John Dalton had vetoed such a bill.

Coleman, whose problem is a progressive past--as a state legislator, he had, for instance, sponsored bargaining legislation for public employes, and in his youth, had been a Rockefeller man--responded joyfully, "If the bill came before me I would take the same action on it."

Robb, whose father-in-law once burst into "We Shall Overcome" to a joint session of Congress, did a tap dance.

He would not veto such a bill, not because he is for it necessarily but because he has pledged to restrict his vetoes to two. He noted that the bill had been voted by a large majority and "represented an important symbol to an important part of our population" and that "sensitivity and understanding is necessary in dealing with it."

Another tycoon inquired if Washington, a predominantly black city, should have two senators. Coleman, gladly crisp, said he was against it.

Robb repented a rare indiscretion.

"Four years ago, I told someone I supported it. I have never mentioned it since. I will have to take whatever barbs and thrusts come from being on the wrong side of that issue."

At the banquet the night before, a Republican manufacturer explained why, although he "couldn't stand LBJ," he intends to vote for Robb. Chuck is "mature," he said, pronouncing the word in the Virginia way--matooah.

"All Marshall says is that Reagan must be supported. But I don't know but what Chuck would back him up just as much. Marshall changes his position from election to election."

Marshall had further sinned against "the Virginia way" at the manufacturers banquet. He wore a business suit. He had intended to have a birthday party for his 12-year-old son in his suite, but his backers were so outraged at the idea that politician won out over parent and he dragged his two small sons to the feast, through which they yawned gamely.

"He's been here the last three years, he knows it's black tie," fumed one of the organizers. "A lot of people were offended."

At the close of the debate, Chuck Robb, "who cain't speak for nuthin,' " as one of his critics put it, nonetheless summed it up well. "What we may be looking at is a contest that evolves into certain characteristics which the individual possesses."

In other words, which one of them better personifies "the Virginia way." Obviously, Robb--who is more elusive--is the truer Virginian. It is better in the Old Dominion to have no opinions at all than ever to have harbored any of liberal taint.

What would his formidable father-in-law think of a Johnson-by-marriage who campaigns on Reagan's coattails? Possibly he would use the same words that came to him in 1968 on hearing that Richard Goodwin had quit him to become Bobby Kennedy's speechwriter: "It's like bein' bit by your own dog."