A Columbia Pike streetcar would spur $3.2 billion to $4.4 billion in development over the next 30 years in Arlington and Fairfax counties, triple the amount that would be triggered by improving bus transit, according to a consultant’s study released Wednesday.

The report by HR&A Advisors said the benefits of building a streetcar line between Bailey’s Crossroads and Pentagon City would far exceed the expected $310 million cost of the project — boosting property values, new construction and tax revenue.

Development encouraged by the streetcar project would result in as many as 6,600 new jobs, according to the study, which was commissioned by Arlington to weigh the costs and benefits of the project.

The county has worked for more than a decade to develop a streetcar in the Columbia Pike corridor to provide more transportation options for a growing population and spur redevelopment along an aging street and community.

Although the line would primarily be in South Arlington, it would reach into Fairfax’s Skyline area around Baileys Crossroads, where thousands live and work. The line would ultimately connect to the Crystal City Metro station, where it would meet another planned streetcar-and-bus-rapid-transit line that will run south to Alexandria’s Potomac Yard.

The bus routes along Columbia Pike are already the busiest in Virginia, and demographers expect thousands more residents and commuters to be using the four-lane road in coming years. Creating a mass-transit option is crucial, planners say.

But the project is controversial in Arlington, where opponents say it’s too costly compared with the $73 million needed for a modern bus line. Critics also say that a streetcar system is less flexible than bus transit.

Proponents, including many developers and retailers, compare the importance of the streetcar with the construction of Metrorail in the 1970s. It has been a key issue in two County Board election campaigns, including one now underway.

Arlingtonians for Sensible Transit attacked the study in advance of its release, predicting that the consultants would tell the county government only what it wanted to hear because the county was paying for the $98,000 study.

“He who pays the piper calls the tune,” said Peter Rousselot, a leader of the anti-streetcar advocacy group.

But HR&A and county transportation officials said that the county had no influence over how the six-month study was structured or its conclusions.

The firm examined 16 other studies that compared the costs and benefits of streetcars against high-capacity, articulated buses in a wide variety of North American locations. It also conducted deeper analyses of four comparable projects.

What the consultants found, said Eric Rothman, president of the company, was “by and large, a positive impact for streetcars and a mixed impact for bus rapid transit and enhanced buses.”

Streetcars could handle more riders, travel as fast as buses and reduce traffic congestion more effectively, the study found. Because developers see streetcar rails and wires as more permanent infrastucture than bus routes, they’re more willing to sink their money into new projects when a streetcar line is built.

With a streetcar line, 80 percent of Columbia Pike will be fully developed in 30 years, the study predicted; without it, development will reach 60 percent capacity at that point.

Development along Columbia Pike as a result of a streetcar system would bring between $375 million and $735 million in new tax revenue to Arlington over the next 30 years, the study said.

How the streetcar would be financed is not clear. County manager Barbara Donnellan said that a combination of state, regional and local funds would most likely be used. A detailed account will be included in the county’s 10-year Capital Improvement Plan, which Donnellan expects to complete in the next few months.