In the year since the largest blackout in American history, utilities have fixed many of the problems that contributed to the breakdown but still have not resolved larger issues that could lead to future outages, according to industry officials, regulators and specialists.

Utilities and operators of the nation's electrical grid said they have done what a post-blackout report suggested to diminish the possibility of a recurrence: cut more trees to prevent them from interfering with lines, upgraded computer systems to give a better view of how electricity is flowing in other regions and provided more training to control-room employees.

The cascading power failure that spread across eight states and into Canada, affecting 50 million people, highlighted that some of the operators running the nation's power grid were not following voluntary rules designed to promote electrical reliability. Jolted by the failures of Aug. 14 -- which disrupted traffic lights, travel and phone service in the Northeast, Midwest and Canada -- utilities and electrical grid operators have been following the rules much more closely, according to the industry and its overseers.

"At least for the short term, we're at a much better state than we were last summer," said Patrick H. Wood III, chairman of the Federal Energy Regulatory Commission, which oversees wholesale power.

But Wood and some utility executives remain concerned that operators of the grid could again stray from the rules as memories of the blackout fade -- unless Congress makes the rules mandatory and approves fines for violators. Even though mandatory rules are supported by the industry and its harshest critics, Congress has not enacted the legislation, which is part of a larger, controversial energy bill.

Some industry specialists said that even if everyone were to follow the rules, problems would remain that could lead to more blackouts.

Most fundamentally, they said, power companies have not solved complications associated with deregulation of the industry over the past decade. Before deregulation, electricity was typically generated closer to where it was used. With deregulation, electricity is increasingly being shipped on high-voltage transmission lines from power plants in one part of the country to consumers who live hundreds of miles away.

In addition, there still has not been significant investment in new transmission lines that specialists say are needed to allow electricity to flow freely from one part of the country to another and provide a route for backup electricity that could limit the scope of a blackout.

"The sorts of things that you need to do to make sure that we're not going to have a blackout are not coming into place," said Michael W. Golay, a professor of nuclear engineering at the Massachusetts Institute of Technology. "The blackout reports and actions that have been taken have really been, in my view, exercises in damage control to try to deflect criticism. We'll see if I'm right when we see if we have more blackouts, which I'm expecting we will."

Industry executives and outside specialists are divided about why there has not been another major outage in the past year. Utility officials credit the improvements they have made and the increased adherence to the voluntary rules. But academics who study the nation's aging power grid, a 200,000-mile network of high-voltage transmission lines, said the reason may actually be a combination of moderate temperatures and good luck.

Homeland security officials also worry that electricity could be disrupted by terrorism. Industry executives said that they have taken precautions and are working with the government. They said that the electrical grid has redundancies that should minimize serious disruptions in the event of an attack on a power plant or transmission line.

In April, a joint U.S.-Canadian task force concluded that the power grid needed to be more closely regulated. A task force report focused blame on FirstEnergy Corp. of Akron, Ohio, whose major transmission lines tripped, causing the failure of the grid.

The report said that "unsafe conditions" that day resulted from violations of the voluntary guidelines by FirstEnergy, one of the nation's largest utilities. The task force concluded that FirstEnergy, which recently agreed to pay $89.9 million to settle shareholder lawsuits partly related to the blackout, should have cut power to some of its customers to prevent the blackout from spreading but failed to do so. The company also failed to trim trees near power lines.

The problems extended beyond FirstEnergy. Investigators found that there was "a systematic breakdown" of planning safeguards and monitoring in Ohio and neighboring states.

One of the projects underway to improve electrical reliability after last year's blackout is a series of audits designed to improve performance. The audits are being overseen by the North American Electric Reliability Council, a Princeton, N.J., voluntary industry organization founded after the landmark 1965 Northeast blackout. Grid operators are in the process of implementing recommendations from the audits, according to the council.

Officials from the council, which also oversees the voluntary regulations, said that utilities have been more attentive to the rules since the blackout, even though they are not mandatory. The council, along with utility officials and grid operators, said that if the regulations are followed, the chances of another cascading blackout will be significantly reduced.

"We think there's much more attention and goodwill on the part of the industry to follow the rules," said Ellen P. Vancko, a spokeswoman for the council. But, she added: "We don't know how long those intentions will last."

Still, some companies have complained that the rules are vague and subject to interpretation. The council is in the process of reworking them.

Some industry specialists said utilities have repeatedly violated the rules -- by doing things such as allowing more electricity to flow through their lines than is allowed -- because that can lead to higher profits. Without legislation making the rules enforceable, specialists said there will be little incentive to comply.

The council, which issues reports about rule violations, recently agreed to begin publicly naming violators, which had not been allowed in the past. The council says doing so will serve as an incentive to follow the rules.

Around the country, utilities and grid operators said they are making changes -- some more noticeable to the public than others. The company that coordinates the movement of electricity on the grid in the mid-Atlantic region, including the District, Maryland and part of Virginia, said it has made a number of changes to increase reliability. A sliver of the area served by PJM Interconnection LLC -- parts of New Jersey and Pennsylvania -- was affected by the blackout.

At PJM's underground control room in Valley Forge, Pa., workers have more technical information available to them about the condition of the grid outside the mid-Atlantic. Control-room workers talk on the phone more frequently with operators in neighboring regions to compare notes, officials said.

Managers said those changes allow controllers to react better to failures and make the system more reliable than it was last August when PJM did not have access to critical information as power failures spread.

"Our ability to see into the systems and take corrective action is much improved," said Audrey Zibelman, executive vice president of PJM.

At FirstEnergy, officials said they have removed more trees, replaced control-room computers and provided more training for employees. On the day of the blackout, workers had not been able to see enough data to react properly and had not received adequate training, the investigation found.

A company spokeswoman, Ellen Raines, said those steps will reduce the chance of another blackout.

Still, FirstEnergy said that the investigation into the outage overlooked problems created by an increase in sending power long-distance over the grid.

"It can create stresses on the transmission system that are unanticipated," Raines said. "It's a different situation than the utilities faced when they operated in what were, in essence, little utility islands."

Some academics said that, as power demand increases and more electricity is transferred, unanticipated problems arise. They favor further study to determine whether there is enough reserve capacity in the grid in the event of a power failure, particularly when large amounts of power are being transferred.

On days when large parts of the country experience spells of cold or hot weather, the chances of complications rise, they said.

"Emergency capacity is being consumed by these silly transfers," said Stephen A. Fairfax, president of MTechnology Inc., a power system consulting firm. "It won't be there when a true emergency arises somewhere."

The problem is not a lack of power plants generating electricity -- it is a lack of lines to transmit the power to areas where electricity is needed, according to utility officials.

Demand for electricity has been increasing far more quickly than the grid has expanded. When electricity was generated closer to where it was distributed, that was not as much of a problem.

Bottlenecks in transmission capacity exist around the country, and power ends up flowing in unplanned directions. Operators have to compensate by increasing the output from their generators in some places and reducing it in others.

Grid expansion and modernization has not kept pace with demand because companies have little financial incentive to build new lines for long-distance transfers of power across their territory, utility representatives said. In addition, homeowners have objected to new lines near their back yards, complaining that they are unsightly.

Some parts of the country, most notably California, already face problems moving power from one place to another.

Officials with the Edison Electric Institute, an industry trade group, said companies would be more likely to expand the grid if there were more financial incentives. The group supports tax breaks in the energy bill.

Others argue that more power lines and plants would not be needed if there were greater efforts to conserve electricity by better insulating houses and using more efficient appliances.

Said Anna Aurilio, legislative director at the U.S. Public Interest Research Group, an advocacy organization: "Energy efficiency is the cheapest way to meet demand."