After 90 minutes of what one observer called “political theater,’’ the planning board voted 4-3 Thursday to reject a proposal by Wal-Mart to build a 140,000-square-foot superstore on Amherst Street to replace the Building 19 store.

Member George Torosian cast the swing vote to deny the project after the board had deadlocked 3-3 on the plan last week.

After the vote, the crowd of about 100 people sat in stunned silence for several seconds before beginning to applaud.

The vote ends months upon months of debate and haggling over the project, which would have been the city’s first Wal-Mart. The fight might not be over, as the retail giant could challenge the board’s decision in court.

Ward 2 Alderman Richard LaRose, city engineer Steve Dookran, and Hugh Moran joined Torosian in opposing the proposal. Chairwoman Bette Lasky, Vice-Chairman Ken Dufour and Steve Farkas supported it.The meeting included several attempts by Andrew Prolman, a lawyer for Wal-Mart, to delay the vote until February or March. In the end, the same four members who voted to reject the plan also voted against the retailer’s request for an extension.

Prolman was standing in for his partner, Gerald Prunier, who was out of town on business. He argued that an extension would allow Wal-Mart to address concerns about traffic raised by Dookran last week.

“This has been a long road to get here,’’ Prolman said, “and we don’t see any reason to rush this issue.’’But Jed Callen, a lawyer for Citizens Action of Southern New Hampshire, a group that has been fighting the project for about a year, said the board closed the public hearing on the plan Dec. 12 and it should stay closed. “The process can go on literally indefinitely,’’ Callen said, “and that is not fair to the public who has to attend meeting after meeting. It is a travesty to prolong this.”

Prolman said immediately after the vote that he couldn’t comment on whether Wal-Mart would appeal the ruling to Hillsborough County Superior Court. Callen, however, said he fully expects an appeal and is confident the board’s decision will be upheld by the court.

“I’m not worried about it,’’ Callen said. “The board’s decision was based on facts.’’

Wal-Mart’s proposal, which first surfaced more than three years ago, generated what many consider an unprecedented uproar among residents. At previous meetings, throngs of opponents showed up at City Hall to voice concerns about traffic, pollution, crime and other disputed effects of “everyday low prices.”

In the final analysis, traffic concerns did the proposal in. Last week, Dookran surprised many when he said Wal-Mart’s $2 million plan to widen Amherst Street was not consistent with a master plan for the road and needed to be redone.

At one point, Dookran and Dufour exchanged barbs. Dufour equated the traffic concerns “bombs.”

The city engineer was clearly offended and said the remarks could be construed as “professional character assassination.’’

The meeting even featured a so called “secret envelope’’ that purportedly contained information related to Dookran’s concerns, but the envelope was never opened because the board had already agreed to stop taking testimony.

Alderman LaRose, who represents the Amherst Street area, made the motion to kill the plan, saying traffic generated by the superstore would be intolerable.