Mary Ches Applewhite's drive to maintain the park-like setting of a six-acre, federally owned parcel in Avondale was crushed this week when the highest bid offered at an auction came from a land developer who wants to turn the area into a housing project.

"They will not be welcomed," said Applewhite, a board member of the Avondale Citizens Association, which led a campaign to keep the property free from development.

The parcel, at 4900 LaSalle Rd. in Prince George's County, just across the District line, has been used for decades by neighboring residents as a recreational site. Part of the old Christian Brothers De LaSalle College, the site was purchased by the federal government in 1976. Since then, the sprawling 17-acre site has housed the Avondale Research Center, a division of the Interior Department's Bureau of Mines.

Last year, acting under an executive order by President Reagan to sell surplus federal land, the General Services Administration determined that six of the 17 acres at the research center were unneeded and should be sold at auction.

Nearby residents immediately began lobbying to keep any new development out of the 30- to 40-year-old neighborhood.

"We have enough congestion here as it is," said Ophelia Daniels, second vice president of the Queens Chapel Civic Association, a District group that joined the nearby Avondale Citizens Association in trying to block the sale of the property.

The neighborhood groups covered the immediate area with signs warning, "No Developers Wanted," and sent petitions to President Reagan and Maryland congressmen and senators. Sen. Charles McC. Mathias (R-Md.) and several county officials have supported the residents' efforts to maintain the area's green space.

But their efforts apparently failed when Kioumars Aghazadeh, a Rockville developer, bid $170,000 for the property. GSA officials, however, said Aghazadeh's bid was below the estimated value of the property, which GSA declined to specify. The federal agency will decide during the next two weeks whether to reject the $170,000 bid, or give the developer one chance to raise his bid.

Aghazadeh, who said he was unsure if he would offer more than $170,000 for the site, said he most likely would begin construction within a year on a complex of single-family detached homes if he is successful in obtaining the property. He said he was unsure of how many homes he could fit on the six-acre parcel.

Aghazadeh said he was aware of the neighborhood opposition to the sale, but decided to buy the property anyway.

"I'm concerned," he said. "Any time you have neighbors opposing you, you generally have problems."

The neighborhood, however, is equally angry with the federal government as with the developer.

Nearby residents said they feel betrayed by the GSA because of a list of assurances that the Bureau of Mines gave the neighborhood when the government bought the property 10 years ago.

Among the assurances contained in the list was a guarantee that "any additional development including site improvements shall acknowledge and preserve the unique campus atmosphere and ambiance of the existing site and building development, including relationships to the adjacent parkland and residential property in Avondale. . . . "

GSA officials, however, said that any agreement between residents and the Bureau of Mines was "unofficial."

Howard DeVane, a realty specialist with GSA's regional office in Atlanta, said the agreement "is not part of the recorded title." He characterized the assurances as being "unreasonable restrictions."

But neighborhood advocate Applewhite said GSA is ignoring the list of guarantees in order to sell the property.

"How can GSA say it was just a piece of paper?" Applewhite said. "GSA has no integrity."

William L. Miller, who oversees the Bureau of Mines' six national research centers, including the Avondale site, acknowledged that his agency did offer the neighborhood a list of assurances when the government purchased the property.

"I thought in all good faith that we'd maintain it as the Christian Brothers had," said Miller, who added that he "shared the concerns" of area residents over the development of the open space.

"We consider ourselves as part of the neighborhood," said Miller, who added that it "was not our intent" that the assurances would be discarded. "Things have evolved . . . to a point where we're not the ones in control."

Neighborhood residents have not been alone in trying to prevent the parcel from being developed into commercial or residential use.

Last year, the National Capital Planning Commission, which oversees construction projects on federal land in the Washington area, reported to GSA that the parcel should be sold "for recreational and open-space use." GSA, however, rejected the NCPC recommendation.

The Maryland-National Capital Park and Planning Commission also tried to buy the property last year for use as parkland. But GSA officials said the park agency's undisclosed offer was considered too low.

At Wednesday's auction, the commission again tried to purchase the site, but stopped bidding at $124,000, $46,000 less than Aghazadeh's bid.

"I'm very disappointed," said Robert Arciprete, the commission's chief of planning, design and research and one of five bidders on the property. "We think it's going to be a loss to the community."

Residents are confident that their support among county officials will make it hard for the developer to obtain a zoning change for the land, which is zoned for open space.

"I think it's going to be an uphill battle for them and for us," said Applewhite, who added that "we want the developer to know that they're not going to get the zoning change."

One of the residents' supporters against the zoning change is Prince George's County Council member Anthony Cicoria, in whose district the land is situated.

Cicoria said that, because of the neighborhood opposition, the property's buyer will have "a very, very, very difficult time" in obtaining a zoning change, a needed step for any development to occur.

GSA officials said they could not understand why the neighborhood was trying to block the sale.

"They haven't told us why they are against the sale except that it should stay as open space," said William Holcomb, a GSA realty specialist. "There's a park on top of the hill behind the research center that more than adequately meets their needs."

But Applewhite asked, "Who is the GSA to decide how many parks we have? It's a situation where GSA thinks it knows what's best for everybody."