To the National Park Service, the best - and cheapest - way to get a portion of Saddleback Mountain that it has long coveted for the Shenandoah National Park is to trade off some less valuable chunks of the park created 52 years ago.

To Rappahanock County residents who own land next to the parcels that may be traded out of the park, that concept is improper, outrageous and probably illegal. The fear the land will be damaged by timbering or development and they know that their own property values are nearly double what they would otherwise be because the land is next to the park.

They and other opponents of the proposed trade of the private Greene County tract for four smaller parcels of National Park land argue that the swap would violate both state and U.S. law.

The resulting conflict has inflamed residents of Rappahannock, triggered a legal dispute between the Interior Department and Congress, and created serious doubts about the government's power to trade away parkland anywhere in the United States.

It has led Rep. Phillip Burton (D.Calif.), chairman of the House Subcommittee on National Parks and Insular Affairs, to ask the director of the National Park Service for "written confirmation that further processing of the proposed exchange will be halted" pending congressional review.

And it has stalled, at least temporarily, three years of negotiations between Shenandoah National Park officials and Saddleback Associates, a partnership made up of Lois Snead, the wife of Virginia Circuit Court Judge Rayner V. Snead who sits in Rappahannock County; Jean McNear, the wife of retired Army Col. Evan A. McNear, the county zoning administrator, and Eric Adamson, Front Royal town attorney and the Sneads' son-in-law.

Shenandoah National Park superintendent Robert R. Jacobsen has wanted the 442-acre Saddleback tract the partnership owns for years. It forms a peninsula of private land in a beautiful, mountainous area north of Swift Run Gap 70 miles west of Washington. It were developed it would "severe off" other prime park land and mar the view from Skyline Drive, Jacobsen said.

According to assistant superintendent William M. Loftis, the Saddleback partners were "interested in the park getting the land and were interested in getting some other land for it."

Shenandoah officials proposed swaps for land in Augusta and Rockingham counties, beginning in 1975, but Saddleback Associates was not interested. A park service proposal to trade a total of 405 acres in three parcels in Rappahannock and one in Warren County awas acceptable to the partnership, and appraisals, surveys and studies for the exchange began.

According to Jacobsen, the appraisers set equal values of about $220,000 on the properties to be exchanged. On May 22, the National Park Service issued a press release explaining the need for the Saddleback land that would be exchanged "for four parcels of parkland which have minimal value for park purposes unless additional adjacent tracts of privately owned land could be acquired."

The release was the first notice of the trade that several adjacent property owners said they had received. The park service had notified the county planning commissions involved, but several owners contend they should have been notified individually.

Led by A. Stanley Thompson, a consulting engineer who had moved from Washington to 170 acres of mountainous land outside Sperryville in 1970, property owners next ot the land that was to be taken out of the park began to protest.

Thompson said that land next to the park was now worth about $1,000 an acre, or $300 to $500 more than similar land not adjoining the park. His three-quarter-mile boundary with the park "was a very important factor" in choosing his land, he said.

The parkland to be swapped is "very fragile land" that would be badly damaged if it were logged or developed, Thompson said.

The park service's assessment agreed, stating that "possible timber harvest and denuding of the area could cause soil erosion . . . If heavy construction were to be carried out, the configuration of the under rock would sufficiently altered so as to make it impossible to return the land to its original state."

Pearl Dodson, another park neighbor, objected on other grounds. When the park was created, a peak on the land to be traded was taken from her husband's father by condemnation.

"They took the biggest part of our land.If they make that trade that land my husband's father owned would go to them (Saddleback Associates). My husband said if that happens he'd never let them come through our land to get to it," she said.

For years there was hatred of the sprawling 191.268-acre park among the people forced from their homes, but that has died now. Thomas Taylor said, and "the park makes very good neighbors. I would like to see it stay like it is."

With the controversy growing, park superintendent Jacobsen scheduled additional hearings and postponed a final decision, but continues to push for the swap.

"I'm looking at the overall health and welfare of the park. I'm much more concerned about the possible development of the tract in Greene County (the Saddleback land) than I am about the exchange parcels." he said.

The Rappahannock land "has little to no public use now or possibly in the future," Jacobsen said. "They are extensions of the private backyards of the landowners. That doesn't mean they aren't beautiful, but in look at the bigger picture they have very much less to offer."

"I can understand the owner's point of view and I sympathize with it, but you have to recognize our vantage point - Shenandoah National Park will be here for centuries and centuries after we are gone. We are looking at the long-term gain for the public. It is my task as a steward of the park to take this longer view," he said.

Thompson, in his attack on the swap, came upon a point of Virginia law that appears to be on his side. The state has a reversion law that requires that land given to the federal government by the state, as was much of the park, must be returned to the state if the federal government ceases to use if for the purpose for the which it was given.

The state code was amended in 1975 at park service request to exempt Shenandoah, but the amendment was deleted from the code in 1976 without Jacobsen's knowledge.

Thompson also has contacted the National Parks and Conservation Association, a citizens' organization set up in 1919 to work for additions to the park system and protect existing packs. Destry Jarvis, administrative assistant for parks there, told Thompson of a federal law passed last year that states "the secretary (of the Interior) may not alienate property administered as part of the national park system in order to acquire lands be exchange."

Staff members on the House Subcommittee on National Parks and Insular Affairs, said that the language was written with the specific intent of barring trades such as the one proposed by the park service in Virginia.

They alerted subcommittee chairman Burton, who complained to the National Park Service. Interior committee staff members now say they believed landowners could be successful in court in blocking the trade under either state or federal law.