In an unusual move, a District-based developer is expected to swap a parcel of land near the Pentagon with Arlington County to make way for a park and put a residential development next to it.

Monument Realty LLC said it will pay the county $25 million and turn over seven acres it owns south of Route 395, near Old Jefferson Davis Highway and Boundary Channel Drive overlooking the Potomac River. In exchange, Arlington will give Monument a roughly five-acre parcel that abuts that land to the south.

Monument said it plans to build an estimated 700,000-square-foot residential complex on the southern parcel. Arlington plans to develop a $90 million park on the northern part of the property, with large pools, soccer fields and other recreational facilities.

"It's a good thing for us because it's the gateway [into Virginia] and it has the best views," said Arlington County Board Chairman Jay Fisette (D). "The land that Monument is getting is closer to the development of Crystal City and more appropriate for a mixed use-type of project."

The deal comes after a year-long dispute between the developer and the county.

Monument bought its site last summer from Equitable Life Assurance Society. The property was once home to the Twin Bridges Marriott hotel -- one of the first Marriott hotels in the area.

The developer filed plans to build a roughly 400,000-square-foot, high-security office complex on the north tract. But Arlington officials rejected the project, saying they didn't like the building's design and wanted to share the parking garage with the public and not reserve it for private-paying office tenants.

Monument sued the county in the fall. In January, Arlington officials proposed the land swap deal with Monument.

"This is a compromise between the two parties," said Jeffrey T. Neal, a principal at Monument. "It gives us the opportunity to redevelop an underutilized property and to do a first-class residential community."

The land swap deal is expected to close in the next nine months. Monument said it would start construction of its residential project at the end of 2006 and would probably complete it in 2008. Fisette would not say when construction on the park would start.