In the madly scrambled world of Virginia politics, three days is long enough for roughly three new candidacies, two withdrawals, one threat of a bolt and the birth of a quasi-draft movement. But ready or not this Saturday in Roanoke, the state's Democrats are supposed to pick somebody to run for the U.S. Senate--or for cover, depending on how smoothly Gov. Charles Robb can glue together enough left, right and moderate wings to call them a consensus.

That's what the governor thought he had weeks ago, when he tapped Owen Pickett as his favorite. But neithr the candidate nor the way Robb handled the anointing was acceptable to party members. Some felt snubbed, some were disappointed in the choice, and others, including L. Douglas Wilder, the state's leading black politician, felt the party was giving blacks short shrift on too many matters of importance to them.

Exit Pickett. Return Wilder. Scattered applause for Robb's helping it to happen, and a mini-rash of euphoria at the revived prospect of the Democrats' following their clean sweep of the top three statewide offices and continued domination of the legislature with the capture of a Senate seat controlled by father and son Byrds for half a century.

But Robb, having been burned once for heavy-handedness, went shy. Instead of seizing an opportunity to rally the party around a rank-and-file favorite -his own lieutenant governor, Richard J. Davis -or another man with statewide appeal -Senate Majority Leader Hunter B. Andrews -Robb backed off. So did big-money fund-raisers. And so did Davis and Andrews. Even the one candidate with some money of his own, Del. Norman Sisisky, a wealthy beer and soda distributor, decided against the Senate race.

Grinning all this while, of course, was the Republican's likely nominee, Rep. Paul S. Trible, who must have wondered whether he'd over have to lift a finger to win the whole thing.

But now the last laugh may be on Trible. Virginia's old guard has decided to revive the candidacy of the man who started everything off in the first place by announcing his retirement from the Senate. Urging Independent Harry Byrd Jr. to reconsider now are former governor and Democratic-toRepublican-Party-hopper Mills Godwin, former Democratic congressman Watkins Abbitt and former Democratic delegate W. Roy Smith. They and others are circulating petitions all over the state in an effort to collect the 10,756 signatures needed by next Tuesday to place Byrd on the ballot as an Independent.

For the Democrats, who had been left staring blankly at an assortment of favorite sons and daughters in need of more foster parents, this may represent a second chance -a chance that the conservative vote will be split between Byrd and Trible.

So once again, what Robb decides to do becomes very important. It will be up to him to broaden his base of advisers and forge the kind of coalition necessary to tack together a majority of the 3,624 convention delegates for Saturday, and then round up all of them for the campaign after that.

With the campaign support of a governor, a liutenant governor, an attorney general and leaders of the state legislature, the Democratic candidate, whoever he or she is, could still have a good run for the Senate.