BOSTON - A federal agency said Friday that the nation's first offshore wind farm, proposed for the waters off Cape Cod, posed no serious environmental threat, bringing it a major step closer to fruition.

A computer-generated image of what Cape Wind, the nation’s first offshore wind farm, would look like from the shore of Cotuit, Mass., on Cape Cod. (Cape Wind Associates, via Bloomberg News) Homeowners and boaters on the cape, including Senator Edward M. Kennedy, Democrat of Massachusetts, have fought the project for eight years, saying it would hurt wildlife, fishing and tourism and spoil the beauty of Nantucket Sound.

Opponents have sued to stop the project, known as Cape Wind, and more challenges are certain, keeping the path to construction bumpy despite what supporters on Friday called a crucial victory.

The Alliance to Protect Nantucket Sound, a group formed to fight the project, suggested that the Bush administration had unscrupulously rushed to approve it before President-elect Barack Obama takes office next week.

"They wanted some kind of a legacy," said Audra Parker, the group's executive director. "Cape Wind is far from a done deal, despite this favorable report."

The federal agency that released the final environmental impact statement on Friday, the Minerals Management Service, is a division of the Department of Interior.

The wind farm would cover 24 square miles - roughly the size of Manhattan - five miles off Cape Cod. From the shore, the 130 turbines, each 440 feet tall, will be visible half an inch above the horizon on clear days, according to Energy Management Inc., the company planning the project. Jim Gordon, the company's president, said that optimistically, construction could begin late this year, and that the wind farm could be producing electricity by the end of 2011.

The project would cost more than $1 billion, Mr. Gordon said, adding that he has spent $40 million since proposing the wind farm in 2001.

"This has been a long, hard road," Mr. Gordon said in a news conference at his Boston offices.

"We think," he said, "this wind farm is going to be embraced by the Cape Cod community, it's going to be embraced by the nation and, most important, it has already encouraged other states to look at developing their own coastal wind resources."

With Friday's release of the environmental impact statement by the Minerals Management Service, the new administration must wait 30 days before issuing a decision. If the decision favors Cape Wind, the federal government can then lease a section of Nantucket Sound to Mr. Gordon's company, according to the Minerals Management Service.

But Cape Wind would still need to wait for several permits, as well as a decision by the Federal Aviation Administration on whether the wind farm would interfere with airplane radar. Past studies by the F.A.A. found no serious threat, but Jim Peters, an agency spokesman, said that F.A.A. officials visiting the site last summer found evidence of possible electromagnetic interference.

Also yet to come are a final statement from the Coast Guard on whether the project would hinder marine radar, and the results of an investigation by the inspector general for the Department of Interior, requested by Cape Cod residents, into the environmental review process.

Mr. Kennedy, whose family compound in Hyannis Port looks out on the proposed wind farm site, has consistently opposed the project on the grounds that it would hurt navigation, the local economy and the environment.

"I do not believe that this action by the Interior Department will be sustained," Mr. Kennedy said in a statement. "By taking this action, the Interior Department has virtually assured years of continued public conflict and contentious litigation."

Aides to Mr. Kennedy made a point of saying Friday that an obstructed view was not among the senator's concerns.

Mr. Kennedy and other critics pointed out that the Minerals Management Service had not yet issued general rules for building offshore wind projects and that their absence continued to make Cape Wind legally vulnerable. Even the American Wind Energy Association, which supports wind projects, said the lack of guiding rules was problematic.

"It continues to be a big concern of ours," said Laurie Jodziewicz, the association's manager of siting policy, adding that the delay in publishing rules "holds up a lot of the projects under consideration right now."

Cape Wind supporters say the project would ultimately supply 75 percent of the electricity for Cape Cod, Nantucket and Martha's Vineyard. But others have cautioned that users' electricity rates will probably rise sharply. Representative Bill Delahunt, a Democrat from Cape Cod who is against the project, said in a statement that it could potentially double power costs for the region.

Gov. Deval Patrick, a Democrat who supports Cape Wind, wants Massachusetts to be a leader in creating alternative energy sources. This week, he set a goal of developing 2,000 megawatts of wind power capacity - enough to power 800,000 homes, Mr. Patrick said - by 2020. The state currently has only nine large wind turbines capable of producing 6.6 megawatts.