PORTLAND — The Portland City Council decided on Monday night to sell about two-thirds of the publicly owned Congress Square Park to private developers, who wish to use the space to expand on the former Eastland Park Hotel.

The deal proposal, which was amended several times during more than two hours of council deliberation Monday night, was approved by a 6-3 vote. Voting against the sale were councilors John Anton, Kevin Donoghue and David Marshall.

After the vote was recorded, several protesters left the meeting and yelled out that the councilors should “Sell City Hall,” and an opposition group Friends of Congress Square Park immediately announced a lawsuit contesting the sale.

“Tonight’s vote is an offensive move on Portland’s park system,” said Frank Turek, president of the Friends of Congress Square Park, in a statement.

“If you remove the emotional aspects of this issue, which I know is very difficult, you have to look at the facts. To me, that’s where my ultimate decision is grounded,” said Councilor Cheryl Leeman in explaining her vote in favor of the sale. “I have a reputation as one who believes in public preservation of open space. However, if you look at the zoning … It’s not a park. It doesn’t have a zoning designation as a park, but it does have a zoning designation as a [business zone].”

Amendments to the sale pact included changes forcing developers RockBridge Capital LLC to pay for the removal and packaging of the historic Union Station clock currently at the site, and that the hoteliers get Planning Board and Historic Preservation Board approval for their conference space addition before the property is officially conveyed.

At-large Councilor Jill Duson said as she went door-to-door in the city, opinions were “running neck-and-neck” on the issue, while District 3 Councilor Ed Suslovic said he saw mostly support for the deal while walking his district — an experience that contradicts recent poll numbers on the issue, which just more than a week ago showed only 31 percent of respondents in that district in favor of the sale.

“From my experience, [feedback has] been overwhelmingly positive [in favor of the sale]. They see a win-win for the city, they see a failed public space, they see an opportunity to bring 200-500 people into the city for events at this center,” Suslovic said.

Councilors Marshall, Donoghue and Anton suggested they received very different messages from constituents they talked to.

“It’s a failed public space because we let it fail,” Marshall said. “This is a public space that really does need an investment. In my mind, it wasn’t a question of whether we should invest in it, it was a question of whether we should sell two-thirds of it and invest in one-third of it, or invest in the whole thing as public space.”

The council arrived at the decision after its second straight tumultuous meeting on the topic. Audience member Erika Elkins was handcuffed and escorted from the council chambers by plainclothes police officers after standing during the early portion of the session and telling councilors she will outbid developers for the Congress Square park.

Elkins refused to sit after being told to by Mayor Michael Brennan, and the council voted to go into recess while Brennan, Police Chief Michael Sauschuck and other city officials approached her and asked her to step out of the room. Sauschuck and two other officers took her into custody and removed her from the meeting after she said she would not.

Elkins said she would pay for the property with money she expects to receive as the result of a lawsuit. Elkins filed a sprawling legal complaint against a slew of defendants, including the Portland police department, four years ago as part of a dispute with siblings over control of multimillion-dollar properties left behind by a deceased parent.

A federal judge ruled on behalf of the defendants in that case in 2010, but Elkins filed a renewed complaint this March with the U.S. Department of Justice, and said she expects to receive $12.9 million if or when her legal effort is successful.

In part in support of Elkins and in symbolic protest of the lack of public comment taken on the sale Monday, some demonstrators stood in the meeting with tape over their mouths. Councilors did not hear public testimony on the subject Monday because they took more than three and a half hours of it at their Sept. 9 meeting.

During that meeting a week ago, the mayor called a recess while another audience member refused to sit down and lower a cardboard protest sign. That demonstrator, Michael Anthony, left the chambers before police arrived to forcibly remove him, however.

A poll on the sale released earlier this month indicated deep public opposition to the sale and sale price. The national organization Public Policy Polling released poll results before the council’s previous meeting on the topic showing that 49 percent of respondents said they opposed the transaction while 34 percent approved.

Only 33 percent of respondents said the proposed sale price is “too high” or “just right,” while 56 percent said it is “too low.”

The poll — of 507 city residents conducted Sept. 5-6 — was commissioned by Portland-based public relations firm Baldacci Communications on behalf of a client who asked to remain anonymous.

Baldacci Communications President Stephanie Clifford said in a statement that their client “had concerns about the sale.”

Perhaps most emphatically, the poll showed that respondents didn’t want the council to have the final say on the subject. Sixty-three percent of survey respondents said they wanted the sale to be decided at the polls by a citywide referendum.

The developers are required in the deal to pay $45,000 to the city for infrastructure improvements at the plaza, including a new 100-by-15-foot sidewalk along that section of Congress Street, and an additional $50,000 to help pay for a redesign of the remaining 4,800 square feet of public plaza space.

The city could rescind the sale if the RockBridge event center design doesn’t receive planning board and historic preservation board approvals by June 1, 2014, among other provisions.

The opposition group Friends of Congress Square Park submitted affidavits on Sept. 6 to begin the citizens’ initiative effort, which would, among other things, change the ordinance governing the Land Bank by creating a new category called “urban open public spaces” and placing 35 properties, including Congress Square Park, in it, according to a press release.

After several days of review, the city’s lawyer has determined the group cannot invoke the citizens’ initiative process because the amendments it proposes conflict with city code and Maine law, according to a city announcement Friday.

On Monday night after the council voted, Friends of Congress Square announced plans to challenge the city’s rejection of their petition in court.