THE FEDERAL AGENCY evaluating the environmental impact of Vineyard Wind provided no explanation for its decision to extend the time period for review beyond Friday, but noted it has until March 2020 to complete its work, several months after the offshore wind developer had planned to begin construction.

Stephen Boutwell, a spokesman for the Bureau of Ocean Energy Management, issued a statement Thursday afternoon saying the agency is continuing to evaluate the environmental impact of the project.

“Proposed offshore wind facilities are major infrastructure projects, and BOEM is still within the two-year review window established under Executive Order 13807 to complete its reviews,” the statement said. “When the work has concluded, BOEM will publish its findings and notify all stakeholders.”

The federal agency published a notice of intent to issue an environmental impact statement for Vineyard Wind in the Federal Register on March 30, 2018, which would mean the two-year window would end on the same date in 2020.

The timing is important because Vineyard Wind is operating on a very tight construction schedule calling for work to begin this year and be completed in 2021. A delay of any length could jeopardize that schedule and put the company at risk of missing key milestones in its power-supply contracts with Massachusetts utilities.

Vineyard Wind posted a statement on its website Wednesday saying that it had been informed that federal regulators “are not prepared to issue” a final environmental impact statement for the 800 megawatt project on Friday as planned.

“We understand that, as the first commercial-scale offshore wind project in the US, the Vineyard Wind project will undergo extraordinary review before receiving approvals,” the statement said. “As with any project of this scale and complexity, changes to the schedule are anticipated.”

Sources said Vineyard Wind officials were planning to meet with officials at the Bureau of Ocean Energy Management on Thursday, but details about the meeting were not available.

Officials in the Baker administration, who have been big champions of the Vineyard Wind project, did not immediately return phone calls Thursday.

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...