AMHERST — Town councilors have delayed a decision on a nearly $10 million increase in the borrowing authorization for the $46.1 million expansion and renovation of the Jones Library, with members saying that they want to wait for a revised agreement with library trustees that ensures taxpayers won’t absorb higher project costs.

After extensive discussion Monday, following more than an hour of public comment in which more than three-quarters of those in the Town Room and participating remotely spoke in favor of amending the appropriation, councilors pushed its vote off to Dec. 18 so that a signed memorandum of agreement is finalized and there is an understanding of how money will flow for the project.

Councilors supported the delay by a 10-3 vote, with District 5 Councilor Ana Devlin Gauthier, District 4 Councilor Anika Lopes and District 2 Councilor Pat DeAngelis voting against postponement.

Town Manager Paul Bockelman told councilors that the project, which will add 15,000 square feet to the 48,000-square-foot building at 43 Amity St., can’t go out to bid in early January without the revised borrowing authorization, which needs support from at least nine councilors.

Bockelman brought a revised memorandum of agreement to the library trustees last week. Trustees tentatively agreed to support it, though they haven’t yet signed it. That MOU spells out how the project is being funded, including the $15.8 million town share, $15.6 million from Massachusetts Board of Library Commissioners grants and $13.8 million from the library trustees, including its capital campaign.

District 4 Councilor Pamela Rooney, though, said even though the $13.8 million balance is a commitment from trustees, the MOU should have flexibility to go beyond that number, in case of higher overall project costs.

“It’s very important that if there is yet another difference in the amount, that the library is not capped at contributing,” Rooney said. “If it came in significantly over that I would want to make sure it is also clear that they will provide those funds.”

For District 3 Councilor Dorothy Pam, constituents are telling her that a new fire station in South Amherst and Department of Public Works headquarters might not happen due to the library project.

“What I think so many people are afraid of is we’re going to be in a position where the town has spent tremendous money, and the library too, and we find out we have to spend more, and more, and more,” Pam said.

Bockelman said if the low bid comes in higher than $46.1 million, and can’t be reduced through cost-cutting, then the bid will be rejected.

“We cannot sign a contract higher than that amount without an additional action by Town Council to provide the funding for the difference,” Bockelman said.

District 5 Councilor Shalini Bahl-Milne said she was concerned about adding language to the memorandum calling on trustees to cover increases in the cost from bidders. “Adding language in the MOU to suggest the project could go higher weakens our position in front of bidders, without adding any benefit,” Bahl-Milne said.

At Large Councilor Mandi Jo Hanneke said a signed MOU is not needed before the Town Council votes. “I don’t see why we cannot trust our fellow elected officials that they will uphold their word on that agreement,” she said.

District 1 Councilor Cathy Schoen said she wants the agreement tightened. “I think the effort to strengthen this wording, even if it’s repetitive, is worth doing,” Schoen said.

But Schoen also said there is no Plan B. “The library needs urgent action,” Schoen said.

Strong support,some opposed

At least 75% of the emails councilors have received have been in support of the higher bond authorization, Bahl-Milne said, with those against it expressing concern about Amherst’s high property taxes.

“As far as the library goes, the increased cost is not impacting the town because the town is still paying what it committed to pay because the library trustees are paying any additional costs above what the town committed to pay,” Bahl-Milne said.

Ginny Hamilton, the campaign manager for the Jones Library Capital Campaign, said the latest two-week delay can slow the giving process, as some potential donors are awaiting the Town Council action.

“Some are waiting to pledge. And those who have made pledges are waiting to donate until the project is certain,” Hamilton said.

Janice Lefebvre of North Prospect Street is one of those who has yet to make a full pledge for the capital campaign, something she said she and her husband will do once the borrowing authorization is finalized.

Speaking against the increase in appropriation was Maria Kopicki of South Amherst, observing the spending could jeopardize other town projects.

“Please do the right thing,” said Jeff Lee of South East Street. “Vote no, and find a more affordable and more democratic way to fix up the Jones Library.”

The opinions in opposition were in the minority at Monday’s meeting. Many of those in the Town Room wore “Building Together” buttons.

Among those who spoke included residents who have previously led capital campaigns and building projects, including Cheryl Zoll, the former executive director of the Amherst Survival Center, who oversaw its move to 138 Sunderland Road in 2013, and Carol Johnson, the former the executive director of Amherst Cinema.