The Arlington County Board, once known for its 5-0 votes and near-unanamity of opinion on how to build the perfect progressive suburb, can no longer agree on whether the promise of an extra $65 million from the commonwealth is a good thing.

In a contentious three-hour session Thursday, the board members traded verbal barbs over the Columbia Pike streetcar project, and whether last week’s announcement that the state of Virginia is willing to pay for half the cost of the line can really be trusted.

“Is this absolutely sure? Do we need to apply for it?” asked Libby Garvey (D), one of two board members who oppose building the $333 million streetcar line, favoring a modern bus system. “Sometimes you get a letter in the mail saying you’ve won up to... It sounds more likely than a sweepstakes, but it’s not a sure thing.”

She and John Vihstadt (I), who also opposes the streetcar, tried to use a normally routine workshop meeting on the county’s capital improvements projects to stop the long-planned transit project in south Arlington. They proposed a series of motions to stop all spending on the streetcar plans, but they lost almost all on 3-2 votes.

The rest of the board agreed to ask the county manager to study whether capital projects of more than $1 million should be subject to the board’s approval. The board also unanimously voted not to use residential taxpayer money on the streetcar, a policy they’ve expressed before.

Tempers frayed as Garvey and Vihstadt tried to stop or delay streetcar project. If it is formally approved at the Saturday County Board meeting, engineering studies will start this fall, county staff said.

County Manager Barbara Donnellan tried to swat down the question of how reliable the state transportation money is, calling it “the most sure transportation funding [I’ve seen], as someone who’s been here 30 years.” She noted that Metrorail was built without funding guarantees.

Vihstadt described the county’s publicity about the streetcar, which includes a series of online videos, to be “a costly and well-scripted Madison Avenue-like public relations campaign to sway public opinion, especially at a time when the funding scheme is in doubt... is an inappropriate expenditure of public funds.”

County Board chairman Jay Fisette (D) called the description “offensive,” and Donnellan said: “If there wasn’t so much misinformation out there, maybe we could do fewer.”

When Garvey argued that adding modern buses to the fleet that already plies Columbia Pike are a “proven” mode of transportation and that streetcars run at half the speed of buses, Fisette fired back “I disagree factually with everything you’ve said in that statement.”

When board member Mary Hynes (D) attempted to argue in favor of streetcars, she and Garvey talked over each other until Fisette, lacking a gavel, slammed a hand down on the board’s table. When Garvey tried to persuade her fellow officials that money devoted to streetcar construction could be used for other purposes, Fisette had enough.

“To sit and say, despite a briefing by our professional staff, that funds are fungible, is just irresponsible,” he said.

Vihstadt argued that the debate, which he characterized as civil and robust, was long overdue on a County Board that had supported the streetcar project without dissent. But in 2012, Garvey, who won a special election without taking a stand on the streetcar, abstained during a crucial vote. Two months later, in throes of her general election campaign, she became an opponent.

Vihstadt startled Arlington’s political establishment when he became the first non-Democrat in 15 years to win a County Board seat this past April. He replaced streetcar advocate Chris Zimmerman, who resigned in February. Vihstadt’s campaign was based on his opposition to the streetcar and other costly capital projects. He’s running against the same Democrat, Alan Howze, in November.

The Columbia Pike streetcar initiative has been planned for more than a decade, and proponents say the public has weighed in many times on its value. It would be built as a joint project, with the state and Fairfax County, running from the Skyline area just south of Leesburg Pike, up 4.9 miles of Columbia Pike to the Pentagon City Metro station.

County officials now want to connect the project to a separate Crystal City to Potomac Yard rapid bus transit line that will eventually become a streetcar line as well. That segment would connect to the city of Alexandria’s bus rapid transit project that will run from Potomac Yard to the Braddock Road Metro station. They hope to have it open by 2020.

It’s more than simply a transit project, however; it’s a linchpin and part of a complex plan to save 6,200 affordable housing units.

A county-funded consultant’s study released in March said the streetcar would generate $3.2 billion to $4.4 billion in new real estate value for Arlington and Fairfax counties over 30 years. It also estimated that the streetcar would produce $455 million to $895 million in new tax revenue for both counties over 30 years, attract 6,600 new jobs within 10 years, and increase state income and sales taxes.

But opponents argue that a streetcar costs too much money for an outdated concept. Buses are much cheaper, bus routes are more flexible and modern buses can carry almost as many passengers as streetcars, they say. They also point out that the streetcars would have to share the right lane of traffic in each direction with other vehicles, so it could add to road congestion.

While county residents are deeply divided on the topic, it’s unclear whether they are evenly divided. The County Board majority has rejected calls for a voter referendum on the topic. Each side says the other is obfuscating and presenting their own perspectives as truth. The difference was on vivid display Thursday.

“A lot that is being said here are opinions, not necessarily facts,” Donnellan observed.