In compact Falls Church, where property values are soaring, a dispute is erupting over what to build on one of the city's remaining undeveloped plots: a park or apartments for low-income seniors.

The city, which is just two square miles, needs more of both. It has 92 housing units for low- and moderate-income residents and a long waiting list of people trying to get into them. Meanwhile, the real estate assessment of the average single-family home reached $527,000 this year, a 23 percent increase from 2003.

But there is also a shortage of parks, which is why some residents oppose the construction of a five-story senior affordable housing facility on a 1.2-acre pocket of green space adjacent to West End Park off Grove Avenue and North West Street.

Clashes between park advocates and affordable housing proponents are becoming more common in the region in places where developable land is scarce. In Falls Church, that tension is felt sharply because of its limited space and the escalating price of real estate.

Families who live near the site of the proposed housing project have long viewed the plot as part of West End Park and feel the city is reneging on its commitment to open space. Many said they were shocked to learn that plans called for such a tall building.

Resident Kathryn Kleiman, for one, pointed out that the mid-rise apartment building would be the tallest structure in that part of the city and said it would not fit the character of the suburban neighborhood.

She said she moved to Falls Church four years ago so her children could attend its school system, known as one of the area's best. She said she chose her house because the back yard bordered West End Park. She hadn't expected to face the prospect of living so close to a mid-rise building.

"This is our only park for several hundred families and over 120 children," said Kleiman. "I'm completely dismayed . . . that we have to focus on one small park that beautifully serves a rapidly increasing young population."

But Carol Jackson, executive director of the Falls Church Housing Corp., a nonprofit agency that develops and manages affordable housing in cooperation with the city, said Falls Church's soaring property values demonstrate the need for more affordable housing. The project would have 62 units and be limited to seniors whose income is less than $36,000 a year, she said.

On one hand, Jackson said, she can sympathize with the concerns of the neighbors. "It's obviously hard for people who live next to the park and have always thought of the entire vacant land as a park. It's definitely a shock to them that the land was slated for development sometime in the future," she said.

But there are few other places to put such a building. Jackson said the only other possibilities are in the heart of downtown Falls Church, but city officials have decided that those properties are too valuable and should be used for commercial development, which boosts city tax revenue and lessens the burden on homeowners.

Members of the City Council said they will try to seek a balance between the competing needs. Council member David F. Snyder said he would like to reduce the size of the structure so that at least half of the 1.2 acres is kept as parkland.

"The neighbors have some very good points about the current project being too big and intruding on too much potential parkland," he said. "But we have a community with higher [housing prices] than average, and we need this kind of housing."

Added Mayor Daniel E. Gardner: "I'm for trying to work out the best balance for the community and for the neighborhood and for senior affordable housing. It's a matter of finding the right scale and scope for the project, and we are working on that."

On Monday, the Planning Commission deferred a decision on the matter until Dec. 6. The City Council is scheduled to vote on the project Dec. 13.