Virginia Gov. Charles S. Robb yesterday urged Republican senatorial candidate Paul S. Trible Jr. to "come clean" and admit that a Trible campaign memo linking Democratic candidate Richard J. Davis to big labor money was a lie.

"It's the same old tactic which, I think, undermines the credibility of the campaign that has to resort to that type of guilt by association," said Robb, underlining the credibility theme that the Davis forces are stressing in this fall's campaign. "I would suggest that they do come clean on the issue."

Robb's remarks were the latest round in the crossfire between the rival camps over the Aug. 11 memo, which has been denounced by Davis forces as a collection of "malicious falsehoods" and for which they have demanded an apology. Trible, however, has declined either to apologize or name the source of the report.

In the memo, which sought funds from Republican supporters, Trible campaign manager Judy Peachee quoted an unnamed source as saying that Davis campaign workers solicited funds from labor union leaders at a recent meeting in New York. According to Peachee's memo, the Davis campaign had asked that the funds be delivered after Sept. 30 to evade reporting deadlines set by the Federal Elections Commission.

The Davis campaign, however, denies that any Davis workers were present at the meeting of the AFL-CIO's Committee on Political Education, held earlier this month, or that anyone solicited funds on their behalf.

Appearing at a state capitol press conference, in which Lt. Gov. Davis named Robb and Attorney General Gerald L. Baliles as honorary campaign cochairmen, Robb said the Peachee memo seemed to indicate that the Republicans were intimidated by the strength of Davis' record as former mayor of Portsmouth and former chairman of the state Democratic party.

"It seems that this always happens when you have a good, sound, fiscally conservative Democrat," said Robb.

Republicans countered that the Davis campaign is shaky and that, as a result, the Democrats were overreacting to the memo, which they said was intended only for party use.

"Dick Davis picked up the tar baby with glee because he wasn't talking about the issues and he was behind in fund-raising," said Neil Cotiaux, Trible's press secretary. " . . . If Dick Davis and the Davis campaign want to play with tar babies, that's their prerogative. But we don't intend to get involved in that."

Many conservative leaders in anti-labor Virginia are already wary of Davis, who as Portsmouth's mayor relied on the backing of the city's blue-collar union members, and the Peachee memo appeared to many Democrats to be a deliberate Republican attempt to capitalize on labor's traditional lack of popularity in the state.

Speaking at the press conference, Davis said he was "seeking support wherever I can find it," but said that the credibility of the candidates was a far more important campaign issue.

"For whatever reasons, there are inaccuracies," he said. "It seems to me that the thing to do is to come forward an admit that 'I Trible have made a mistake.' "

Cotiaux, Trible's spokesman, labeled the controversy a "manufactured, bogus issue cooked up by a campaign whose candidate is behind," and said the Trible campaign stood behind the memo.

"The governor certainly has a right to express his opinion on any subject . . . but it's natural for him to come to the aid and comfort of his own party's Senate candidate," he said.