As Rep. Stan Parris looked out of the chartered Cessna 421, the sweeping urban sprawl of Fairfax County and the rest of his 8th Congressional District faded into the distance.

Some 450 miles ahead lay this cool green mountain country of Southwest Virginia where Parris hoped he might plant the seeds for a campaign as the Republican candidate for governor in 1985.

The trip was billed as an effort to support GOP candidates in the Nov. 8 General Assembly elections. During a long day in this coal-scarred valley, Parris would extol the virtues of a two-party system (it is a heavily Democratic area), dole out $500 to a State Senate candidate and mingle over cold-cut hors d'oeuvres at two receptions.

But privately, the day was part of a low-key, but intense early effort by the two-term congressman to position himself to replace Democratic Gov. Charles S. Robb, who after one term cannot succeed himself.

"The executive mansion is about as high as you can rise in Virginia," the 54-year-old silver-haired conservative said on the flight to Wise County. "You would have to be pretty callous not to take that possibility of running seriously, but," Parris said in a quick disclaimer, "my first order of business is reelection to Congress" in the fall of 1984.

The prospects of a Northern Virginia congressman running for governor has sparked early interest in the 1985 campaign, particulary since the state Democrats have so far failed to come up with a major challenger for the other major race in the state--next year's Senate contest against incumbent Republican John W. Warner.

Parris, who must overcome downstate suspicions and win over Richmond's corporate and legal powerbrokers, is taking his cue in part from Virginia's other Republican senator, Paul Trible, who campaigned from his Tidewater congressional district for more than two years before winning his seat last fall.

Parris, who won reelection to Congress by barely 50 percent of the vote last year, turned aside questions about whether his early campaign for governor could hurt his chances for reelection next year.

"It's not hurting me," he said. "If we don't increase the number of Republicans in the General Assembly, it will impact on the 1984 elections." State Sen. Richard Saslaw (D-Annandale), who is running for reelection, is expected to challenge Parris next year.

Parris said he will spend about $45,000 on travel and donations to local races this fall--paid with funds from his state-registered Commonwealth Leadership Committee. He has traveled several times since the summer to six of the state's 10 congressional districts and has more than 40 visits scheduled before Nov. 8.

"As large as the state is," said Parris' chief aide, Richard Leggitt, "you really have to do quite a bit of field work early. It gives us the kind of intelligence and background on whether to make the decision. You have to get out to see how people react to you."

Parris already employs a full-time fund-raiser, and another aide updates a growing list of more than 200,000 names of potential supporters.

Several Republican leaders say Parris and former state delegate Wyatt Durrette, who lost a bid for attorney general in 1981, are the two strongest potential candidates for governor behind former Gov. John N. Dalton, who is recuperating from lung cancer surgery in Richmond.

Both Durrette, who is also traveling extensively around the state, and Parris have said they would not run against Dalton, who is now practicing law in Richmond. Dalton has said he wants "to be a factor" in 1985 but has not indicated he actually would run for his old job. Friends say his health would be a major factor.

Durrette has hired an aide, Mark Obenshain, the brother of late Richard Obenshain, architect of the Republican revival in the 1970s, to update his campaign lists.

The early campaigning by Parris and Durrette is similar to jockeying on the Democratic side between Attorney General Gerald L. Baliles and Lt. Gov. Richard Davis, who each would like to succeed Robb. Davis lost out to Robb in the early stages of the Democratic campaigning in 1981.

Marshall Coleman, the Republicans' unsuccessful 1981 gubernatorial candidate, is interested in another race, but is expected to have difficulty rebuilding his support, several party leaders said yesterday.

Parris' eight-hour trip to Wise and Buchanan counties Monday cost about $1,000 for the six-passenger plane in addition to the $500 contribution to lawyer Gene Compton, who is waging an uphill battle against incumbent Democrat John C. (Doc) Buchanan for the State Senate seat from the 40th District.

In Wise County, Parris stuck mainly to pep talk cliches, such as supporting candidates with "fire in their belly," and avoided controversial issues on strip mining and whether he supports a proposed coal slurry pipeline.

In Buchanan County, Parris sped past burning coke ovens and mine shafts as he was squired around by Sheriff Auburn Ratliff, one of the few Republican officeholders here. Parris did not publicly discuss his plans for the governorship and said he sought no commitments in private conversations.

Only a few dozen people showed up at both campaign stops, but Parris came away with a new list of several hundred names, some offers of help and even the use of a local coal operator's plane for future visits.

It was, Parris said, the nitty gritty work "that can make or break a campaign."