When Jeff and Emma Jane Saxe signed a contract to buy a new $130,000 house in the Hampton Forest subdivision in Fairfax County almost 21 months ago, they expected to be celebrating last Christmas in the new home. But construction delays forced the Saxes and their young son Ben to spend Christmas 1984 in their old home.

The construction troubles mounted this past year and now, at Christmastime 1985, the Saxe family once again won't be home for the holidays.

Their furniture is in storage, and the family dog named Coffee has a temporary home in Stafford County. The Saxes, who now are living in what Jeff Saxe describes as a "cramped apartment" in Reston, sold their old home in Annandale because they expected to move into their new one. It stands unfinished at the end of a mud-filled cul-de-sac.

The Saxes said they are disgusted with promises from the builder, Rockville-based Aldre Inc. The Saxes said they have been given many different completion dates only to have each one pass without the two-story traditional home being finished.

"We can't move people in without a street in front of their houses," said Jay Alfandre, a spokesman for Aldre, which is building and selling homes at Hampton Forest, situated off Lee Highway and west of Fairfax City.

Completion of the houses apparently has been delayed by a complicated series of events involving improper road construction, the discovery of methane gas on part of the site and the refusal of county officials to issue occupancy permits while the problems remained unsolved. About a dozen families have been affected by the lengthy delays, but the Saxes' case is the most severe.

While Aldre Inc. is building the houses, Rocks Engineering, a McLean-based firm, is the developer for the project, county records show. The house the Saxes have contracted to buy is almost finished. But it sits along Hampton Forest Place, which is unfinished. Alfandre said road problems are the responsibility of the developer, Rocks Engineering.

A spokesman for Rocks Engineering had no comment on the Hampton Forest situation, saying only that "Aldre has handled all the sales."

Alfandre said, "We are moving people in as quick as we can. We have 120 to 130 houses either under contract or settled out there." The site development plan being shown to potential buyers today calls for at least 189 houses to be built in the development.

The Saxes said they signed a purchase contract in March 1984, with an expected completion date set for near the end of last year. At the rate things are going, the Saxes apparently will be moving into the house nearly two years after they signed the contract.

Asked when houses might be ready for occupancy, Alfandre said settlements are "imminent," but he declined to be more specific.

According to Fairfax County Department of Environmental Management records, the project has been plagued with problems in the past eight months. In early February, county officials "put a 20-day hold" on some lots because "there was naturally occurring methane gas" at the site, according to the agency's deputy director, William Rucker. He said developers solved that problem, which is created by decaying organic materials and occurs at other building sites.

Saxe said he was never told about the gas problem.

On April 5, the Virginia Department of Highways and Transportation told Fairfax officials that the entrance built by Rocks Engineering from Lee Highway into Hampton Forest did not meet state safety standards, according to county records. That led to the county's decision not to issue occupancy permits for new units until the situation apparently was resolved in early September, county records show.

Michael Frey, administrative assistant to Supervisor Elaine McConnell (R-Springfield), in whose district the project lies, said there was a "total blind spot at the project's entrance off of Lee Highway . The developer had to cut back the crest of the hill."

Alfandre said Aldre "kept people informed" as much as possible. But Saxe disputed that. "I have never gotten a phone call from them," he said. "The only information we got was through my calling them."

Alfandre said he is sympathetic, but that anyone unhappy could have gotten out of the contract without surrendering any deposit money. Saxe said he stuck with the deal because the builder kept giving him completion dates that would have matched the time it would have taken him to purchase another new house.

Alfandre said the delays may pay off for some buyers, because interest rates projected for early 1986 settlements are below rates that prevailed when houses originally were scheduled for settlement. Nonetheless, Saxe said that any savings has not been worth the stress or the strain that the delays have generated for his family, even though he admitted that "interest rates would definitely be better."

Alfandre said, "I can appreciate their aggravation, with the holidays coming. It hurts me. It does. We don't like to be this far off. Normally we develop our own lots. We will never get into this situation again."