Beckoned by everything from the offer of a motel "prayer room" to the whistle-blowing call of a flamboyant populist, Virginia Democrats gathered here last night to select a U.S. Senate candidate who could lead the party out of its past decade of defeats.

Virginia is the only state in the nation that has failed to elect a Democrat to the Senate or the governor's office in the past 10 years. But many Democrats said yesterday they are confident that last week's nomination of conservation Richard D. Obenshain as the Republican Senate nominee may give them the opportunity to turn their fortunes around.

To help make the selection easier, delegates to the party's convention were offered a "prayer room" by "born again" candidate G. Conoly Phillips of Norfolk and an enthusiastic endorsement of State Sen. Clive L. DuVal II of McLean by defeated Democratic gubernatorial nominee Henry E. Howell.

Because of his image as an unabashed conservative, Obsenshain is regarded by most Democrats here as the most vulnerable of the candidates the Republican Party could have offered.

As the Democrats gathered, the three men considered to have the most committed delegates were: former state attorney general Andrew P. Miller, DuVal and Conoly Phillips, a Norfolk city councilman. Each has cast his claims to electability in strikingly different terms.

Miller is one of only four Democrats elected to statewide office since 1966 and has said unequivocally that his moderate-conservation image, name identification and political momentum make him the only candidate with a hope of general election success in what he calls this "do or die situation" for the party.

DuVal, a moderate-liberal in the party spectrum, has contended he has been untouched by the divisive struggles between liberal and conservative Democratic wings of the last decade. Phillips surged into contention in April on a tide of support from delegates attracted by his Christianity. He makes the case that he is a fresh face who can rescue what he calls a "flat" party with an infusion of "excitement."

Perhaps more than any other candidate, Phillips recognizes that he owes his success so far in the Senate race to the low fortunes of the Democratic Party in Virginia. "If the party was not in such bad shape," he said, "they wouldn't need me."

Three other candidates are given a chance to win the nomination if the convention turns into a search for a compromise. They are former Fairfax County supervisor Rufus Phillips, former state delegate Carrington Williams of Fairfax and state Sen. Hunter B. Andrews of Hampton.

The two remaining candidates are considered to be out of the running. They are former Fairfax supervisor Frederick Babson and Falls Church feminist Flora Crater.

Conventional political arithmetic dictates that Miller will be the nominee when the convention ends tonight. When he came to Williamsburg yesterday, he and his opponents expected him to receive 40 to 45 percent of the 2,797 delegate votes on the first ballot, a commanding plurality in what is really a six-way race.

This has led many office holders and party officials here to dismiss the chance of an upset. As Fairfax delegates for DuVal and Rufus Phillips checked into the Ramada Inn West, State Del. Richard D. Saslaw of Fairfax, who said he will vote for Miller, nodded toward them and said:

"A lot of people are coming here they're going to be disappointed."

Nevertheless, there are enough uncertainties in the convention to inspire hope in the underdogs.

"The two principal uncertainties," candidate Williams said, 'are whether the Miller vote will hold solid if he doesn't get a majority on an early ballot and what the Conoly Phillips delegates will do if he drops out."

Conoly Phillips is presumed by the other candidates to have firm control over as many as 400 delegates who came here yesterday interested in him as a Christian candidate. Phillips himself has vowed to stick with the party if he is not nominated and has told his delegates to stay in the convention even if he drops out of the race.

However, other candidates have found it hard to obtain second choice commitments from the Phillips followers. "When we have talked to them, we generally get the answer that they are coming just to support Conoly," Miller said.

The Phillips campaign also has provided a contrast with conventional political styles. His hospitality suite at the Fort Magruder Quality Inn features a prayer room rather than a bar. "The only spirits we are offering is the Spirit of the Lord," a campaign spokesperson said.

A number of delegates were forced to commit themselves to candidates other than their true first choice in order to be chosen at city and county caucuses to attend the convention. They are bound for one roll call and are expected to shift to their actual preference on the second ballot. "To the managers and the candidates, that will be the real first ballot," Sherman Webb, manager for Rufus Phillips, said.

Proposed rules permit all eight candidates to remain in the race through four ballots, a circumstance that Miller himself said could delay the victory he expects until the fourth roll call.

Miller has called on his supporters to rally at the College of William and Mary football stadium this morning and Conoly Phillips has invited his to a prayer breakfast. The other candidates are concentrating on personal appeals to uncommitted or wavering delegates.