Fairfax Republican Rep. Stan Parris, fresh from a decisive reelection victory, said today he will announce here on Wednesday his long-expected campaign for the 1985 GOP nomination for governor of Virginia.

Parris, 55, famed for his fund raising and computerized congressional mailings, said today he is more electable than his two likely rivals, Wyatt B. Durrette, a Richmond lawyer and former Fairfax County legislator, and J. Marshall Coleman of McLean, the former state attorney general.

Coleman was the GOP candidate who lost the race for governor in 1981 to Democrat Charles S. Robb. Durrette, who is expected to announce for governor in two weeks, lost a bid to become attorney general that year.

"The question really is who is most likely to have the kind of success we must have next year," Parris said in an interview.

Just elected to his fourth term, Parris defeated Democratic State Sen. Richard L. Saslaw of Fairfax by more than 23,000 votes in the 8th Congressional District, which includes parts of Fairfax, Stafford and Prince William counties and the city of Alexandria.

Parris has acknowledged that he is not well known throughout the state, but indicated that his Northern Virginia base will be crucial. He noted about 38 percent of the state's vote in last week's elections was cast in the Northern Virginia's 8th and 10th districts.

The congressman will announce a "Parris for Governor Committee" on Wednesday and hold a traditional one-day campaign swing through several cities in December.

The Parris organization has assumed a lease on what was the Reagan-Bush campaign headquarters in downtown Richmond and it is expected to announce a start-up war chest of more than $200,000, almost twice the amount reported by either Coleman or Durrette.

A conservative, Parris took a swipe today at the state Democratic Party which is in the midst of a three-way race for governor, has a senior black state senator running for lieutenant governor and a woman trying to become the state's first female nominee for attorney general.

"I worry about some of the combinations of the other side that I think would impede substantially" the traditions of Virginia government, Parris said.

Parris said in response to a question that the overwhelmingly white vote President Reagan received in Virginia and the overwhelming support blacks showed for Democrat Walter F. Mondale was part of a realignment of the two parties "that will have an effect on future elections."

Parris said, however, that he would not rule out campaigning for black votes. "We are going to go after everybody."

Both Durrette, who has been campaigning for more than a year, and Coleman have expected Parris' announcement. Neither was available for comment today.

Parris is expected to begin an immediate mail campaign to about 25,000 Republicans who have been delegates to party nominating conventions or have been involved in previous state GOP conventions. The party nominee will be selected at the 1985 convention May 31 and June 1 in Norfolk.

A key party meeting will occur in early December in Staunton when party leaders will set up rules for mass meetings that will select convention delegates. Some of those mass meetings could be held as early as February.

Parris said he decided to run today after meeting with about 15 supporters at his Fairfax County house. Among the participants were John (Til) Hazel, Fairfax County developer; William Stanhagen of Manassass, GOP national committeeman, and John S. Alderson Jr. of Roanoke, who led the Reagan-Bush campaign in Virginia. Alderson has dropped plans to run for lieutenant governor, Parris said.