Community and hospital leaders had cause to celebrate yesterday as the Elm City’s largest — and most controversial — construction project in years finally broke ground.

Yale-New Haven Hospital began construction on its new cancer center facility, slated for completion in late 2009, on Wednesday with a ground-breaking ceremony attended by Mayor John DeStefano Jr. as well as Yale-New Haven President and CEO Marna Borgstrom.

“In just over three years, we will return to this spot and open the doors of this magnificent facility that will rival any in the nation,” Borgstrom said in a press release.

The construction process will proceed in accordance with the terms of an agreement signed by community, city and hospital leaders in March, Service Employees International Union spokesman Bill Meyerson said. The SEIU has been talking with hospital workers about organizing, and Meyerson said the hospital has been respectful of the SEIU’s right to do so under the agreement.

“We’re pleased,” he said. “We have no qualms at all. It seems to be going well.”

Community Organized for Responsible Development member Phoebe Rounds ’07 said community members are generally pleased with the progress of unionization and the execution of the community benefits agreement, once a contentious issue, which includes continued community input through a neighborhood planning committee.

Although community leaders were not included in the earlier planning stages before the agreement was reached this spring, Rounds said community leaders have been continually involved over the past few months. She said community input on solving traffic and parking issues will become an especially important factor in the construction process during the next couple of years.

“The folks in CORD are very happy with the community benefits agreement that was reached, but that was just a first step,” Rounds said. “We look forward to continuing to work with the hospital to find solutions to those issues.”

Rounds said that the unionization drive began July 1 and that although no date has been set, a vote will be held in the near future.

The new $467 million facility will house all of the hospital’s oncology services in one building, which will streamline the patient care process already established in the current Yale Cancer Center, hospital spokesman Rob Hutchison said. In addition to accommodating 112 patient beds, the building will include a specialized women’s cancer center and one floor each for diagnostic and therapeutic radiology.

“Once constructed, the 14-story, 497,000 square-foot cancer hospital will be the most comprehensive cancer care facility between Boston and New York City, offering patients state-of-the-art care and treatment,” Hutchison said.

The integration of different components of cancer care to provide high-quality treatment is of key importance to the new building, Borgstrom said.

“This new cancer hospital will be a place of compassion and hope, where the latest research breakthroughs can be applied at the bedside for the benefit of all our patients,” Borgstrom said. “Today we say to all people living with cancer and to every member of our community, ‘This is the day that we start building hope.’ That is our mission and that is our promise.”

The ground-breaking ceremony also included Dean of Yale Medical School Robert Alpern and Bishop Leonard Williams, along with hundreds of supporters.