Nearly 100 conservative Republican donors -- the wealthy true believers who helped finance Ronald Reagan's White House drive last year -- gathered at a Capitol Hill breakfast yesterday morning to hear why they should do the same for the GOP's Virginia gubernatorial nominee, J. Marshall Coleman.

Over cold $50 eggs and warmer political rhetoric, Coleman repeated for the crowd one of his main campaign themes: that the Virginia race would, "rightly or wrongly, be viewed as a referendum on the popularity of the Reagan administration." And he accused his Democratic opponent, Lt. Gov. Charles S. Robb, of "nitpicking" the president's budget-cutting program and opposing Reagan's tax cut bill.

To underscore those points, Reagan political aide Lyn Nofziger showed up briefly to pledge "an all-out effort" for Coleman and his Republican running mates. "I don't want there to be any doubt in anybody's mind where the White House stands in this election," said Nofziger. "We think it'd be a disaster for the people of Virginia to give us the other guy."

Reagan aides previously have scoffed at the notion of the Virginia contest as a referendum on the president because Robb, a conservative Democrat, has expressed general support for Reagan's policies. But Nofziger made clear that the White House was committed to Coleman and that Reagan himself will campaign in Virginia. "We will be there when you need us, Marshall," said Nofziger.

Reagan's favorite pollster, Richard Wirthlin, who this year is polling for Coleman, also was on hand to drop broad hints that his latest survey showed the GOP state attorney general edging ahead of Robb, who in previous polls had been up by 10 to 15 points.

Wirthlin would give no numbers and campaign manager Anson Franklin would only say "we're smiling," but Coleman and his staff have been spreading the word privately about the poll, which followed a $200,000 television and radio campaign designed to enhance Coleman's name identification with voters.

Robb campaign spokesman George Stoddart later denied the charge that Robb opposes Reagan's tax-cut bill. "He has never said that," said Stoddart, adding "the Coleman disinformation mill is working overtime." But Stoddart did concede that Robb has said balancing the federal budget should have priority.

Coleman has repeatedly suggested that Robb, who is married to the late president Lyndon Johnson's daughter, Lynda, would flood Virginia with out-of-state money-raised through his family connections.But yesterday it was Coleman who was appealing to such out-of-state interests as General Motors, Monsanto and Boeing, which were among the companies with officials at the $50-a-plate breakfast.

"I'm really touched by this turnout," quipped Coleman, "but not as touched as you all are going to be."

The gathering was sponsored by the Fund for a Conservative Majority, which last year was the country's third largest independent fund-raising group and which has already pledged at least $100,000 to Coleman's campaign. Fund Chairman Robert Heckman said the breakfast raised about $7,500 but the real prize is a bigger pot of gold. "The idea here is to get other conservative PACs involved by introducing them to Marshal," said Heckman.

The struggle for money is a key element in the race, in which both sides expect to raise more than $2 million. Unlike federal election law, Virginia law allows corporate donations and imposes no limits on gift size -- features that the Coleman campaign has stressed in fund-raising letters to out-of-state Republicans.

Most of yesterday's attendees appeared to have already made up their minds about Coleman. "You don't show up at 7:30 in the morning and pay $50 unless you're supporting someone," said Earle Williams, president of BDM Corp. in McLean.