PORTLAND — There was great anticipation on Monday for a decision by the Portland City Council of whether to sell about two-thirds of downtown Congress Square park for an adjacent hotel development.

Instead, after three and a half hours of impassioned public testimony, and a brief break when Mayor Michael Brennan asked for police to remove a protester who refused to put down his sign, the council voted unanimously to postpone its choice until Sept. 16.

The developer, RockBridge Capital LLC, has agreed to pay the city nearly $524,000 for a 9,500-square-foot section of Congress Square. RockBridge is partnering with New Castle Hotels on a $40 million-plus renovation of the former Eastland Park Hotel, next to the square.

With the additional Congress Square space, the developers plan to add a one-story venue for meetings and other events at the historic hotel, which they plan to reopen in December as the Westin Portland Harborview hotel.

If the council approves the sale, approximately 4,800 square feet of Congress Square would remain as a public plaza.

Opponents — including members of the OccupyMaine movement and the citizens’ group Friends of Congress Square Park — say the city should revive the park as a public space, and argue a sale would set a dangerous precedent of turning public space over to private firms.

These opposing groups have launched an online campaign to raise $1 million to outbid RockBridge for the property.

“We can, we should and we must repair our park and reinvent it for everyone to share,” said Portland resident Wellington Lyons on Monday.

“There’s so much talk about how that park is dilapidated and unused,” said sale opponent Matthew Coffey. “I’ve heard that that park used to be flooded in the winter for ice skating, that there were concerts and movies there.”

Proponents of the deal — which include the Portland Community Chamber, Portland’s Downtown District and the city-formed nonprofit Creative Portland — argue the new development will revitalize a long-neglected site that has become a hangout for drug users.

“I am sick to death of discouraging business in Portland,” local businessman Adam Zimmerman told the council. “This space has been an issue for 10 or 15 years. So I ask, where have these people been for the last 10 or 15 years? The only proposal on the table right now is from RockBridge.”

Longtime Portland resident James Melanson told the council that he and others have been targets of aggressive panhandling and derogatory comments from drunks and drug abusers there.

“One of the things that makes a park is that it’s a safe place, and that it’s accessible by everyone in the city,” he said. “Congress Square Park is not a safe place. … This is a perfectly reasonable proposal.”

A poll on the sale released Sunday indicates deep public opposition to the sale and sale price. The national organization Public Policy Polling released its results Sunday, showing that 49 percent of respondents said they opposed the transaction while only 34 percent approved of it.

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.

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 terms of the sale on the table force RockBridge to continue using the additional structure for meetings and events for at least 10 years before being allowed to convert it into more hotel space.

The developers are also required 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 would 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.

When the city council meets again on Sept. 16, public comment on the sale will not be allowed, leaving the multiple hours of testimony — and tense atmosphere — on Monday as perhaps the last words on the issue.

Early in Monday’s meeting, demonstrator Michael Anthony entered the council chambers with a large cardboard sign reading, “Don’t sell our park.” Brennan told him to sit down with his sign or place it on an easel provided to speakers at the meeting.

Anthony repeatedly answered, “I understand,” and “I hear you, Mayor Brennan,” but he continued to stand and hold the sign over his head.

After multiple warnings, Brennan called for a recess, approved by a 6-3 vote, and then asked to have police called to have Anthony removed.

With the meeting paused, Anthony yelled at councilors, accusing them of initiating the sale talks with the developers.

“They’re not listening to their constituents,” he called out. “Who do you represent?”

Anthony left before police arrived.

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