Brazil slashes top railway rates 25 pct - regulator

* Heavy cargo rates to drop from maximum by 30 pct on avg

* First revision since concessions started 15 yrs ago

BRASILIA, Sept 6 (Reuters) - Companies that ship cargo by railway will see their average maximum freight rate reduced by 25 percent, Brazil's national transport regulator said on Thursday as it announced the first revision of rates in the sector in 15 years.

The appreciation of real against the dollar in recent years has exacerbated what economists refer to as the "Brazil Cost", which includes some of the world's highest energy rates and taxes, stifling bureaucracy, a nearly inoperable legal system and poor infrastructure.

Since the economy stagnated a year ago, President Dilma Rousseff has been trying to attack these problems that she sees as obstacles to competitiveness of local industry and sustainable growth.

The reduction in rail rates is part of the first revision of rates for the sector, the agency said, adding that ceiling rates for heavy cargoes such as iron ore would fall 30 percent on average.

"Today, prices charged are below the maximum rate. In some cases, there will be an effect on the contract," said Fabio Barbosa, the head of cargo transport at the transport agency known as ANTT.

The new breakdown of rates will be published in the government's Official Daily Register on Monday and the new tariffs will go into effect 15 days later.

Rousseff is expected later on Thursday to announce a plan that will bring down energy rates for industry to help it compete with the recent flood of imports.

The change in railway freight rates will affect 11 operators of railway concessions in Brazil that extend over 28,000 kilometers of track. They include companies such as America Latina Logistica and MRS Logistica.

This was the first revision of rates for the railway sector since the start of the modern concession model 15 years ago. The ANTT is expected to revise rates every five years or so from here out, Barbosa said. (Reporting by Leonardo Goy; Writing by Reese Ewing; Editing by Bob Burgdorfer)