W. Roy Smith, a well-connected Richmond businessman who last year played a key role in the election of Democratic Virginia Gov. Charles S. Robb, yesterday announced that he will join with former Republican governor Mills E. Godwin to work for GOP Rep. Paul L. Trible's U.S. Senate campaign.

The combination of Godwin and Smith is expected to send a strong signal to the influential conservative independents who have been closely identified with retiring Sen. Harry F. Byrd Jr.

Republicans heralded the announcement as a "major turning point," saying that it gives their candidate a significant advantage in what has thus far been a rather sluggish race against his Democratic opponent, Lt. Gov. Richard J. Davis.

Davis' press secretary, Will Marshall, said he was "unimpressed" by such an assessment.

Other Democrats, while conceding that Smith's support could assist Trible's fund-raising efforts, argued that it would make little difference to most Virginia voters.

"This doesn't necessarily make it easier for [Trible] to win the election," said Del. Warren G. Stambaugh, an Arlington Democrat. "In terms of influencing the election--who knows or cares who Roy Smith is?"

In the announcement released by the Trible campaign office yesterday, Smith and Godwin said that they will co-chair the steering committee of a group called "Virginians for Trible," and pledged to "urge their friends and all Virginians to join them."

The announcement went on to say that the group will be composed of "predominately non-Republicans from every section of Virginia who believe that sound, responsible and conservative government can best be served by choosing Paul Trible to succeed Sen. Harry S. Byrd Jr. . . . ."

"The impact of this statement can't be overstated," said Trible spokesman Neil Cotiaux. "For those who read the old Godwin tea leaves, this is a pretty strong statement."

Smith and the state's "coalitionists" were credited last year with giving Robb's campaign a sizeable financial boost, and their defection would be a blow to the financially troubled Davis campaign. Davis, a 60-year-old mortgage banker who was thrust into the race in June with no fund-raising organization, had raised only $32,465 to Trible's $520,983 as of last month.

"This is a very significant group of gentlemen," conceded state Sen. Majority Leader Hunter B. Andrews (D-Hampton). "We saw this last year with Chuck Robb . . . Certainly we're going to have to work hard and organize."

A Davis adviser, veteran Democratic advertising man Robert Squier, said the announcement did not come as a surprise to the Davis campaign.

"I personally talked to Roy Smith about it three weeks ago. I think they've just been holding back," Squier said. He said he believed the Republicans had postponed Smith's announcement in an attempt to counterbalance a recent Peter Hart poll that had shown Davis leading Trible by five points.

Neither Godwin, whose conversion to Republicanism in 1973 set off a mass migration by conservative Democrats, nor Smith could be reached for comment yesterday. While Godwin had earlier indicated his public support of Trible, Smith had reportedly been "taking his time," one Republican said.

While it is impossible to fully gauge the power of Smith, a former chairman of the state House Appropriations Committee, and the handful of wealthy conservative businessmen who with him make up the "Main Street Crowd," the group is widely believed in Virginia to be the heir of the once mighty Byrd machine.

Two other members of the group who have announced their support for Trible are Robert H. Spilman, chairman of Bassett Industries, who like Smith was rewarded for his Robb campaign work with an appointment to the influential Governor's Economic Advisory Council this spring; and Thomas Leggitt of South Boston, a key Robb fund-raiser.