A developer owned property that Arlington County wanted for its North Tract recreational complex. The county owned a plot the developer wanted for new homes. So, like sports teams making a midseason deal, the two sides arranged a compromise.

They traded.

The land swap, an unusual arrangement announced earlier this month, will give Arlington a seven-acre parcel that county officials say will enhance the $100 million North Tract complex. In return, the developer, District-based Monument Realty LLC, will acquire five acres from the county where it plans to build residential high-rise units. The county says those units will boost the redevelopment of Crystal City.

As part of the transaction, Monument also has agreed to pay $25 million to the county, which officials say will help defray public costs for the North Tract, a park and swimming complex planned for 30 acres of industrial land just south of the 14th Street Bridge in Crystal City. County officials have hailed the project, the most expensive recreational venture in Arlington's history, as a rare chance to build a large-scale recreation complex in a county where open space is at a premium.

But opponents of the project, which was approved by the county board last year, have questioned the price tag and raised concerns about traffic and the environment, since a small portion of the land is contaminated with lead.

The deal resolved a year-long dispute over the seven acres Monument is giving to the county; that land is south of Interstate 395 near Old Jefferson Davis Highway and overlooks the Potomac River. Monument filed plans to build an office complex there, the county rejected the project and Monument filed suit. The property is known as the "Twin Bridges" site because the Twin Bridges Marriott was there.

Earlier this year, Arlington officials proposed the land swap, in which Monument will give the Twin Bridges parcel to the county in return for the five-acre parcel that abuts that land to the south. The lawsuit is expected to be settled after Monument closes on the purchase of the county's property and has a development plan in place. That process is expected to take as long as a year.

"This is a win-win," said Arlington County Board Chairman Jay Fisette (D). "We will now have $25 million that we did not have before to make sure the North Tract recreational facility in the end is truly world class."

Jeffrey Neal, a principal at Monument, agreed that the two sides "made a good trade."

"The property we will end up developing is very attractive, and this puts the Twin Bridges site in public hands, which is a good use of that property."

He said Monument was "happy to contribute" the $25 million for public use but acknowledged that it "was a good business decision for us." Under zoning laws, Monument can construct larger buildings on the property it is acquiring than it could have erected on the property it is trading.

The land swap also won initial, if wary, praise from some in the county who had questioned the cost of the North Tract complex. "It makes a lot of sense," said Wayne Kubicki, a member of Arlington's Fiscal Affairs Advisory Commission. He said, however, that despite the $25 million infusion, he fears the North Tract project will go over budget.

"This is going to be very expensive, and they don't have a handle yet on what it's going to cost," he said.

County officials said the project remains on budget, although they acknowledged that the rising cost of steel and other construction materials could boost the price. The county originally said construction would start in 2006, but the start has been pushed back to early 2007.

The county is expected to sign a contract soon with two architectural firms to design the first phase of the project, which consists primarily of a 173,000-square-foot aquatic and exercise center with four pools, basketball courts and a fitness center, and two lighted soccer fields. But county officials said the land swap will delay the design process at least several months because the aquatic center will be built on the parcel the county is acquiring from Monument.

The second construction phase calls for a 600-space parking garage, two more fields and an expansion of the recreation center to include a four-court gymnasium, an elevated running track, racquetball courts and a climbing wall. The project includes a bike path, a playground and areas for birders and train-watching.

The mostly vacant North Tract land sits a few thousand yards from Reagan National Airport and the 14th Street Bridge and affords a sweeping view of the Washington Monument and Roaches Run Waterfowl Sanctuary.

As a result of the land swap, the project will cover 30 acres instead of 28. County officials are particularly enthusiastic about being able to build the aquatic center on the parcel they are acquiring from Monument because of its views of the monuments.

"This will be a signature building for Arlington," said Erik Beach, the county's North Tract project manager.