In the exhilaration of his smashing triumph over conservative Democrat Ed Lane four years ago, Virginia's newly elected attorney general J. Marshall Coleman observed that "Virginians don't vote for the more conservative candidate, they vote for the more moderate one."

It was a lesson Coleman either chose to forget, or disbelieve, this year, in his campaign for governor. He staked his ground to the right of his former self, and to the right of the eventual winner, Democrat Charles S. Robb, even though in 1977 both won handily by being less conservative than their opponents.

After nine months of criss-crossing Virginia, listening to politicians and talking to voters, I have arrived at the heretical conclusion that the Old Dominion is no longer the bastion of southern conservatism it once was. Its rapidly growing, mobile population, typified by the sophisticated independent residents of Northern Virginia, includes many voters who never heard of former two-term governor Mills E. Godwin, much less care what he thinks.

Thus, when Godwin's belated, lukewarm, racially tinged blessing was laid on Coleman a week before the election, it brought voters out of the closet, all right, but they were previously unenthusiastic blacks and liberals who voted for the more moderate Robb.

No one on the winning Democratic slate of Robb, Lt. Gov. Richard J. Davis and Attorney General Gerald L. Baliles, is truly a conservative, unless you limit philosophical designations to views on fiscal policy. And in this day and age, everyone hoping to be elected is a fiscal conservative.

At no point in the campaign did Robb attempt to portray himself as more conservative than Coleman. And even in the areas where Robb's views alienated liberals, such as his support of the right-to-work law and opposition to collective bargaining for public employees, he allowed Coleman to stand to the right of him. Where Coleman promised to send in state police to patrol non-union coal mines, Robb was content to say that he would uphold the law; when Coleman argued that the Voting Rights Act should be scrapped, Robb said it only needed modification; and when Coleman attacked Robb for favoring ratification of the proposed constitutional amendment to give the District of Columbia full voting representation in Congress, Robb, even if he may have flinched, stood firm.

This is not so much to praise Robb for sticking to principles as to suggest that Robb and his strategists--even though Coleman attempted to label them outsiders--had a better feel for the mood of Virginians than did Coleman's home-grown advisers, who managed to convince him that a moderate- to-progressive Marshall Coleman wasn't electable.

The argument against moderation is tested, to be sure, by the state's conservative 10-member delegation in the House of Representatives. But even there, none of the state's representatives match the stridency of many New Right congressmen. And the composition of the delegation is volatile. Liberal Democrats Joseph L. Fisher and Herbert E. Harris, ousted in the Reagan landslide, are rubbing their palms in anticipation of rematches next year against Frank Wolf and Stan Parris, and freshman Wolf has been moderating his own conservative views in recent votes and pronouncements.

Whether this month's election was an aberration or a harbinger of continued movement to the middle of the political spectrum may be answered in next year's race for the Senate in Virginia. Many Republicans were counting on incumbent Harry F. Byrd Jr., the only independent in the Senate, to seek re-election as a Republican. But in light of this month's Democratic sweep, if Byrd runs at all, and that is still unknown, it likely will be as an independent again. The Democrats surely will challenge the scion of the conservative Byrd machine with a moderate, perhaps with Andrew P. Miller of Alexandria, who narrowily lost in 1978 to John W. Warner, or former senator William Spong of Williamsburg, who lost to William L. Scott.

Republicans then would face a dilemma: should they sit it out, and give Democrats another chance at a statewide victory, or put up their own conservative nominee and give Democrats 2-to-1 odds to test the depth and breath of Virginia conservatism. With the results of this year's election, the GOP doesn't suffer for a lack of potential nominees--but all have conservative credentials.