Question: How many Virginians does it take to change a light bulb ?

Answer: Four. One to change the blub and three to tell him how good the old bulb was .

The joke may be a bit timeworn, but according to one of the state's most respected political analysists, it still is the most accurate way of saying that in Virginia politics, tradition is everything.

That's a lesson Lt. Gov. Charles S. (Chuck) Robb of McLean and the state's Democrats should heed. Last week Larry Sabato, a leading political analyst in Virginia, unwrapped a poll that many in the party were saying was too good to be true.

A quick look at the Old Dominion's political history may prove them right.

The poll showed Robb, the Democrats' likely gubernatorial nominee, with a commanding 44-to-29 percent lead over his likely Republican rival, state Attorney General J. Marshall Coleman. For a party that has been losing elections faster than autumn leaves falling along Skyline Drive, that should have been welcome news.

But Sabato was quick to add that Virginia is replete with defeated Democrats who had early leads in their races: Henry L. Howell led Gov. John N. Dalton until late in their 1977 campaign; Andrew Miller had Sen. John W. Warner in the dust until the final moments of their 978 contest.

Indeed, it's only when the leaves begin to change their colors that the true allegiances of Virginia voters become known. And invariably the Democratic preferences that show up in early polls give way to Republican candidates and the sway of a GOP organization that Sabato, as assistant professor at the University of Virginia, regards as one of the best in the nation.

For Robb, the first Northern Virginian to hold statewide office in recent decades, the warning from Sabato said in his poll, "will find his lead a difficult one to maintain at all, much less in its present dimensions, as the campaign progresses."

There are historical reasons why many nominal Virginia Democrats would rather switch than stick with their party. Virginia has been Democratic for most of the 20th century, and shaking any tradition in the state is about as easy as selling a Tennessee ham in Smithfield.

But starting in the late 1960s, many Virginians -- especially the local officeholders who held the state Democratic Party together -- began to realize that the conservative principles they clung to were being endorsed by Republicans.

What's more, Republicans were discovering some natural turf in the state's fast growing suburbs, areas that were alien to Democrats, whose homes were mostly in the small towns and downs-state farm lands.

Virginia's Democratic Party structure began to weaken after the state's infamous poll tax was declared illegal by the Supreme Court and thousands of new voters, many of them poor and black, joined the electorate and pushed the Democratic Party to the left.

The dam burst in 1972 when the new voters effectively excluded Gov. Mills E. Godwin from the state delegation to the National Democratic Convention. eWith his pride wounded and his longtime friend, Sen. Harry F. Byrd Jr., already out of the party, Godwin took the only step he believed possible: He became a Republican.

Few things in Virginia politics have been the same since. Godwin's transformation made formal the realighment that had been occurring in statewide elections and, perhaps more than most Democrats realized at the time, accelerated the growth of the GOP.

If Godwin made being a Republican respectable, then Robb this year faces the challenge -- one the sportswriters would call awesome -- of restoring the sheen to his own party's label. Robb, the "Prince Charming" of the Johnson White House, already has gone a long way toward doing that, wooing back old-time Democrats and, perhaps more significantly, winning the support of many suburanites.

It is the votes of those people -- residents of tract housing in Fairfax, Prince William, Virginia Beach and Henrico County -- that Sabato believes hold the key to the 1981 elections in Virginia. Robb, he notes, is the first Democrat in recent years to make inroads there, pulling about 51 percent of the suburban vote in his 977 race against state Sen. Joe Canada, a Virginia Beach Republican.

But Robb faces some potentially serious problems. Coleman has made his own inroads among black voters and in Northern Virginia, Robb's political home. And as most every Democrat will acknowledge, any Democrat must win strongly both with blacks and Northern Virginians to offset losses in conservative downstate regions.

The is another factor that may have a major impact: personality. Coleman is a wily politician, willing to move swiftly across the political spectrum to caapture votes. But Robb, according to Sabato, is too much the consensus candidate; he wants 99 percent of the voters to like him and seems baffled, even hurt, when his actions alienate anyone.

"Coleman knows there are political trade-offs in an election and is willing to take them," Sabato says.

It will be up to Robb to convince Virginians the state's political bulb needs changing, and that he alone can do the job.