THE TENTATIVE agreement reached by D.C. Mayor Vincent C. Gray (D) with D.C. United to build a new soccer stadium in Southwest Washington involves a complicated set of land swaps, tax abatements, leveraged developments and legal stratagems. But if officials are able to pull it off, this deal would secure a badly needed new home for Washington’s Major League Soccer team and help spur economic development in neighborhoods on both sides of the Anacostia.

Mr. Gray unveiled Thursday a $300 million plan whereby D.C. United and the city would split costs on a 20,000-seat stadium at Buzzard Point on the waterfront near Nationals Park. The team would pay for construction of the stadium while the city would pick up the costs of assembling and preparing the land, which it would lease to D.C. United.

Particularly inventive is the District’s plan to swap property it owns, including the Frank D. Reeves Municipal Center in Northwest’s 14th Street corridor, for Buzzard Point land now owned by others. Workers at the Reeves Center would move to a municipal center that would be built in Anacostia, in Ward 8. This would allow the city to finance its costs without using its limited borrowing capacity, while Ward 8’s struggling neighborhoods would get a boost from the new center — much in the way the Reeves Center helped to serve as a catalyst for development on 14th Street 28 years ago. The Reeves Center has outlived its usefulness, so the prospect of a new mixed-use development that will add to the vibrancy of the neighborhood and return the property to city tax rolls makes sense.

The mayor was clearly ebullient at the news conference announcing the deal. That’s understandable, given D.C. United’s tortured history in finding a facility that better serves its sport and fans than does its current home, aging RFK Stadium. But those efforts, dating to 1996 and including threats to bolt the city, should serve as a warning that announcing a deal is not the same as realizing it.

A huge jigsaw puzzle,” is how City Administrator Allen Y. Lew characterized the Buzzard Point plan — and a lot of pieces are still missing. Only one of three Buzzard Point landowners has reached a tentative deal with the city. The actual costs of acquiring the land and cleaning it up must be determined. Transportation logistics need to be sorted out. And approval will be needed from the D.C. Council, which, if the debate over the construction of Nationals Park is an indicator, will produce what The Post’s Mike DeBonis called “a good deal of hand-wringing and debate.”

There’s no question that the council must take a careful look at the proposal and ensure the city’s interests are protected. At the same time, it must not lose sight of the benefits this public investment could realize for the District. It needs look no farther than the transformed community around downtown’s Verizon Center or the area near Nationals Park to appreciate what a sports stadium can do for even those who are not fans.