Despite a strong showing of local support, Downtown Crossing — New Haven’s biggest construction project in half a century — hit a legislative snag at a public hearing Thursday as aldermen voted to send the proposal back to the City Plan Commission for reworking.

Members of the Board of Aldermen’s joint finance and legislation committee held a public hearing Thursday evening to discuss the $135 million project, which would replace sections of Route 34 with urban boulevards and erect a 10-story, 225,000-square-foot medical office tower in the cleared space.

Local business leaders, education officials and community activists voiced strong support for the proposed zoning changes and land disposition agreement under review at the meeting. But ultimately, rather than voting on the legislative package and passing it on for a critical vote by the full Board, committee members decided to send the project back to the City Plan Commission after public testimony questioning the development’s effect on local neighborhoods and raising concerns over how the zoning changes have been advertised.

“The position of many people on the Board is that right now, we aren’t seeing everything as clearly as we would like, and we want to know how this is really going to help the city,” Ward 3 Alderman Ohan Karagozian said at the hearing. “There’s no guarantee that the jobs this project promises to create will go to New Haven residents, and the long-term effects on traffic are unclear.”

Finance and legislation committee members heard testimony from 6 to 7:30 p.m. regarding the proposal to zone the site as a new business development area, and testimony continued for several hours afterward on the land disposition agreement that would transfer the 11 acres of land freed from Route 34 to real estate developer Carter Winstanley. Under the proposal, the city, state and federal government would contribute a combined $35 million clearing and improving the 100 College St. site for construction. Winstanley Enterprises would be awarded ownership of the land and spend an estimated $100 million building a parking garage and a biomedical office tower at the site.

City officials tout the plan as not only an opportunity to generate new jobs and tax revenue but also to reunify the downtown area and medical district now bifurcated by Route 34.

Many local residents who spoke at the hearing highlighted these benefits as well as the opportunity to grow New Haven’s science, technology, engineering and mathematics, or “STEM,” economic base. William Placke, CEO of the Start Community Bank in New Haven, said the Downtown Crossing project targets the Elm City’s “competitive advantage in bio-tech” and expands the “knowledge industry that is the future of the city.”

A group of Gateway Community College officials and students, including college president Dorsey Kendrick, also spoke in favor the project at the hearing, pointing out that many Gateway graduates go on to work as lab technicians or other medical services personnel after graduation.

“Coming from a personal perspective, it’s not easy as a college student to make a decent living, a lot of jobs are not promised to us when we leave,” said Tyler Harris, a Gateway student. “I think this project is a tremendous idea, and for college students like myself, we will have more career options.”

But aldermen ultimately voted to send the proposal back to the City Plan Commission after Marjorie Shansky, a lawyer whom Urban Design League president and Downtown Crossing critic Anstress Farwell brought to the hearing, pointed out potential problems with the way the zoning change had been presented to the public. Shansky said “public notice” was deficient, and when a zoning hearing is planned, enough details must be advertised so individuals can decide if they wish to attend. She argued that the notice for the hearing, titled “New BD-3 zone and related amendments and map amendment” was inadequate. Given the scope of the project, she said, these mistakes necessitated a “do-over” from the City Plan Commission stage.

Aldermen agreed with Shansky as well as earlier opposition and decided by 7:25 p.m. to push the Downtown Crossing project back in the legislative process. Despite the setback for the proposal, Shansky said it was important to “get it right” when it comes to such significant city construction work.

New Haven is home to 39 of Connecticut’s 52 bio-tech firms.