A proposed wind-energy project designed to send massive amounts of electricity from Aroostook County through southern Maine has been put on hold, due in part to the discovery that a technical glitch in transmitting that power could black out portions of southern New England.

The proposal involved hundreds of wind turbines with a total output of 800 megawatts, equivalent to the former Maine Yankee nuclear plant in Wiscasset.

The developer's decision to stop work on that project may threaten plans for a separate $625 million transmission venture that would serve as a conduit to move renewable energy south from northern Maine and Canada. The transmission project would have carried the wind-power energy from Aroostook into the New England regional grid.

The uncertainty comes as the state and the incoming Obama administration are promoting renewable energy as a way to reduce the nation's dependence on oil and cut down on emissions associated with climate change.

Maine set ambitious wind-power development goals last year. And this year, the regional grid operator -- ISO-New England -- is launching a study of how to reliably integrate anticipated, big bursts of wind power into the system.

Some of the information surrounding the wind project and transmission venture is confidential and out of public view. But documents filed with the Maine Public Utilities Commission and interviews by the Portland Press Herald/Maine Sunday Telegram show that questions about the wind project had been growing for months and came to a climax in December.

The documents are filed in a case at the PUC involving Central Maine Power Co. and Maine Public Service Co. The two utilities have joined to develop the Maine Power Connection, which would close a 25-mile gap between Maine Public's service area in Aroostook County and CMP's wires to the south. Currently, Aroostook County isn't connected to the New England grid.

The connection could spark competition in the county between power suppliers. It also would create a new path to send renewable power to New England cities from northern Maine, initially from a project proposed by Aroostook Wind Energy LLC. The company is a subsidiary of Texas-based Horizon Wind Energy LLC, which itself is owned by a major Portuguese utility.

Aroostook Wind has invested millions of dollars and has leased or optioned tens of thousands of acres in northern Maine, according to documents. It has identified 1,200 megawatts of ready wind potential. For starters, it was studying the impact of connecting 800 megawatts to the proposed Maine Power Connection line.

But the study began to turn up unexpected trouble last fall. In public documents, the trouble is described as "stability problems."

Aroostook Wind doesn't spell out in those documents what this term means, and an attorney representing Aroostook Wind couldn't be reached for comment Tuesday. But people familiar with the details said that this problem contributed to the company's decision to suspend its work on the project.

One of them, an intervenor in the case, was willing to summarize the issue in a general way: Under certain circumstances, a sudden interruption of the power flow could cause parts of the regional grid to shut down, according to Gordon Weil, a utility consultant. The problem could be triggered by a technical problem or natural disaster in Maine, he said, adding that computer models showed the problem might occur down the line in Massachusetts.

"Eight hundred megawatts is a lot of power on a single line," said Weil, a former Maine energy director.

Engineers have so far been unable to come up with a solution, Weil said. "This is a much bigger technical problem than anyone thought," he said.

For the past month or so, Weil and other intervenors at the PUC, including water companies and consumer-owned utilities, have been arguing that the problems are so great that the Maine Power Connection can't go forward and the case should be closed. They are pushing for an early termination to keep the utilities from recovering additional costs from wholesale and retail customers, a provision allowed by federal rules.

Their position may have been strengthened on Dec. 31, following a letter to the PUC from lawyers for Aroostook Wind.

The letter says the company has told CMP and Maine Public Service to stop work on impact studies related to the project. It cites "cost estimates and related data."

It also blames changes in the wholesale power market for making the project uneconomical, a reference to today's low oil and natural gas prices. The company said it wasn't giving up on future wind generation in the county, however.

Representatives from both utilities declined Tuesday to discuss what led to Aroostook Wind's pullout. Documents they filed on Dec. 31, however, refer generically to "impediments in southern New England to the integration of the output of the wind farm proposed by Aroostook Wind Energy."

CMP and Maine Public Service aren't giving up on the Maine Power Connection.

In documents at the PUC, the utilities refer to a possible technical fix that may solve the stability problem. They also are considering a smaller project that moves less generation, or different ways to pay for the project.

They are asking the PUC to defer any decision until March. The PUC could deliberate the case as early as next week.

"We'd like to keep the docket open," said John Carroll, a CMP spokesman.

Carroll also stressed that, whatever happens to the northern Maine connection effort, it won't reduce the need for a larger, $1.4 billion project in southern and central Maine to replace and upgrade the existing transmission system. That proposal, called the Maine Power Reliability Program, is proceeding at the PUC on a separate track.

The Maine Power Connection case has heightened concerns over what experts call "grid stability."

In Texas, which has more wind generation than any other state, lights almost went out last winter when the wind suddenly stopped blowing and power into the grid fell off unexpectedly. Operators had to temporarily shut down service to industrial customers to prevent rolling blackouts.

"Is there a signal that the (Aroostook Wind) study is giving us about being able to integrate a large amount of wind into New England?" asked Kurt Adams, chief development officer at First Wind, a major North American wind developer. Adams, a former PUC chairman, said more study is needed to calculate how much wind power New England's transmission lines can handle.

First Wind is operating and developing smaller projects in Maine that aren't dependent on the Maine Power Connection, including two in Aroostook County.

The incoming Obama administration is expected to aggressively encourage wind power development. Also, a task force appointed last year by Gov. John Baldacci set a goal of making Maine a regional leader in wind development, producing 2,000 megawatts by 2015 and 3,000 megawatts by 2020. Much of it could be exported out of the state, with some portion coming from offshore wind farms. The task force estimated that Maine has more wind power potential than all the other New England states combined.

These and other ambitions, along with the issues being identified in Aroostook County, have the operator of the regional grid taking notice. ISO-New England declined to discuss the Aroostook Wind situation, but is planning its own study this year on how to integrate more wind into the generation mix. By one count, more than 1,800 megawatts of new wind projects already are in various stages of development, said Marcia Blomberg, a grid spokeswoman.

"Wind is a variable resource," Blomberg said. "You want to make sure you can operate the system reliably."