A Pentagon City development that could bring five new office buildings, including a 22-story high-rise, to the skyline south of the Pentagon got an important approval Saturday from a unanimous Arlington County Board.

The board agreed to Vornado/Charles E. Smith’s plans to build as much as 1.8 million square feet of commercial space on nine acres of vacant land, one of the largest undeveloped parcels close to downtown Washington.

The project also includes 50,000 square feet of retail space, a 300-unit hotel, completion of 12th Street across the property, a streetcar maintenance facility and a public “green area” between the buildings.

Vornado plans to build a streetcar connection along the new 12th Street, between the proposed Columbia Pike streetcar line and a Crystal City streetcar line. It hopes to turn that new stretch of street, which has been a missing link for years, into a walkable, urban destination and better connect Pentagon City with Crystal City.

County officials said they don’t expect developers to complete the project for at least 10 years.

The Arlington County Board gave unanimous approval to PenPlace, a development that would include buildings as high as 22 stories, a 300-room hotel and a public park.

Although board members endorsed the proposal in five separate unanimous votes, agreement didn’t come easily.

Nearby residents had pushed to require the project, dubbed PenPlace, to include at least one building of apartments or condos, but the board members decided that there was sufficient existing or planned housing in the area.

The deal, which had taken three years to negotiate and six hours to discuss Saturday, almost fell apart in the midst of the vote.

Vornado had promised to pay Arlington $15 million within a year if the county would transfer development rights from Long Bridge Park to the PenPlace land. That transfer allows Vornado to build a bigger, denser and potentially more lucrative project than current land-use rules permit.

But Vornado threatened to delay payment and work on infrastructure until all the political hurdles were cleared. The disagreement was settled after County Manager Barbara Donnellan publicly committed that the county’s work would be completed within a year.

“This has been pretty wearing, even by the usual scale of these things,” said board member Chris Zimmerman (D), who earlier expressed suspicion about Vornado’s ability to build distinctive structures instead of “300-foot refrigerator boxes.” Although each building will have to undergo the county’s site-plan approval process, the proposal Saturday “leaves an awful lot of things to be determined in the future. I lack the kind of enthusiasm I’d like to have here.”

PenPlace, presented as an example of the kind of transit-oriented mixed-use development that Arlington strives for, lies along Army-Navy Drive between South Eads and South Fern streets. It had once been the Virginia Baseball Authority’s preferred site for a major league ballpark.

In 2003, the Arlington board rejected that proposal in favor of a long-sought conference center within a mixed-used development. Vornado bought the land in 2007.