It's hard to say which is more startling. That a developer in Phoenix is threatening -- by Thursday, no less -- to knock down a 1952 house designed by Frank Lloyd Wright. Or that the house has until now slipped under the radar, escaping the attention of most architectural historians even though it is one of Wright's great works, a spiral home for his son David.

The prospect of its demolition has suddenly galvanized preservationists, as these crises often belatedly do. They are pursuing a two-pronged attack, trying to get the building designated a landmark in a process scheduled to reach the City Council on Nov. 7, although in Arizona, where private property rights are strong, landmark status is really just a stay of execution, limited to three years. After that, the owner is free to tear the place down. So the other prong of attack is to find some preservation-minded angel with deep pockets who will buy it from the developer.

Wright designed this 2,500-square-foot concrete home for David and his wife, Gladys, on a desert site facing north toward Camelback Mountain in a neighborhood called Arcadia. The area, known since the 1920s for its citrus groves and romantic getaway resorts among old Spanish colonial and adobe revival homes, was increasingly subdivided after the war and filled with new custom-designed ranch houses. But the Wright lot still had its orange trees. The architect took advantage of them by raising his son's house on columns, to provide views over the orchard. Wright chose a spiral design akin to the Guggenheim Museum's. He had drawn plans for the Guggenheim by then, but it was still some years away from construction.

Wright configured David's house to look both inward and out, twisting around a central courtyard, but also facing onto the surrounding desert, with views of the mountain.

The developer's plan for the site involves subdividing the lot and erecting two or more new houses.

"There is no house quite like this one, with its mythic content," is how Neil Levine, an architectural historian and Wright scholar put it the other day.

How could such a house go largely unnoticed? David and Gladys didn't want their home in a residential neighborhood to be a museum, and so not many architectural scholars or even Wright experts ever got inside it, to see the rug and chairs and mahogany woodwork that Wright devised. David died in 1997 at 102; Gladys in 2008, at 104, leaving the house, no longer in mint condition, to granddaughters who sold it to a buyer promising to fix it up and live in it. But the buyer did neither, and the place, on its 2.2-acre lot, went back on the market. In June, a developer called 8081 Meridian bought it.

"The place was uninhabited for four years and it had never been placed on a watch list," said John Hoffman, managing partner of 8081 Meridian. "We didn't close on the property until the city approved a lot split. The line through the property went through one end of the house, so it was an indirect approval for demolition."

That was his interpretation, although demolition requires separate city approval, and in any case before the sale closed, the landmark process was underway.

The threatened deadline derives from a demolition permit that a staff member in the city development office issued to Hoffman and his partner, despite the fact that officials had flagged the house to ensure no permit would be issued. Planning authorities learned of the permit and voided it after the demolition company called to check that it was valid. Hoffman maintains that the permit is legal and that it expires Thursday.

It may be that the demolition threat is being used as leverage to drive up the price. Hoffman said 8081 Meridian rejected a cash offer floated several weeks ago from an anonymous out-of-state Wright lover that was put at slightly more than $2 million.