In the face of what some Virginia Republican Party leaders see as Ronald Reagan's eroding strength in the state, the former California governor's campaign yesterday announced formation of a three-member team that will criss-cross Virginia on Reagan's behalf.

The announcement that former Northern Virginia congressman Stanford Parris, former Fairfax legislator Wyatt B. Durrette and Winchester publisher Thomas T. Byrd are hitting the campaign trail came amid general agreement that George Bush is making inroads into what had been an overwhelmingly pro-Reagan state four years ago.

"I think Bush is doing well in Virginia," said Republican strategist William Royall. "You hear more people, especially in Richmond, talking about him.

"I would not bet money . . . that Reagan will be able to hang on to first place," said Royall, a Bush supporter.

"Absolutely Bush is making inroads," said one prominent uncommitted Northern Virginia Republican who asked not to be identified. "A heck of a lot of people I knew as Reagan people in 1976 have switched to Bush. Reagan has been taking this state too much for granted."

This year's state convention to select 21 at-large delegates to this summer's Republican National Convention in Detroit is scheduled to be held June 5 and 6 in Richmond. Thirty other delegates will be at congressional district meetings before that.

Four years ago Reagan swept Virginia's GOP convention, receiving 35 of 51 delegates to the Republican National Convention. Former president Gerald R. Ford received 16 delegate votes.

Reagan strategists denied that the formation of their three-member group -- officially called Advocates for Reagan -- was a reaction to a strong challenge by Bush.

"If the Reagan people didn't campaign, they'd be accused of assuming victory like they did in Iowa," said Nick Panuzio, chairman of the Fairfax County GOP and a Reagan adviser. The speakers group "shows their desire to build a strong statewide organization."

"We're running a Reagan campaign, not a campaign in response to another candidate," said Reagan's Virginia campaign manager Bob Hausenbluck. "We have an organization in every congressional district in the state. Besides, I don't know that George Bush has the staying power to carry a state convention in June."

Durrette, a former state delegate who is reported to be considering a race for the GOP nomination for attorney general, agreed.

"Iowa will not be repeated," said Durrette, referring to Bush's decisive victory in that state's delegate selection caucuses last month. "Reagan lost in Iowa because he did not campaign properly and because George Bush concentrated on that state."

Durrette is not the only regular worker who is interested in political office. There is speculation that Byrd, son of Virginia Sen. Harry F. Byrd Jr., an independent, will seek the GOP nomination for lieutenant governor in 1981 and that Parris is considering challenging the Democrat who beat him in 1974, Rep. Herbert Harris, in this fall's election.

But while the Bush and Reagan forces are busy lining up support in Virginia, many well-known Republicans have not yet declared who they will back.

"I'm staying out of that briar patch," said Fairfax County Board Chairman John F. Herrity. "Right now I'm a dedicated neutral. I belong to the ABCK Club -- Anybody But Carter-Kennedy."