BALTIMORE -- The derailment and fire last month involving a chemical-laden freight train in Baltimore is the latest in a series of rail accidents, on the rise since 1997, about the time that several multibillion-dollar mergers left the rail industry financially strapped, the Baltimore Sun reports.

That timing is no coincidence, safety advocates, economists, and union leaders say. Maintenance has suffered, they say because of merger-related layoffs that have reduced the number of inspectors who monitor tracks and equipment. Rail traffic, meanwhile, has grown steadily, with trains carrying increasingly heavy loads.

Officials point out, however, that the rate of accidents has slowed this year.

No one can say what role, if any, track conditions played in the derailment on July 18 of a 60-car CSX train carrying hazardous chemicals through a tunnel in downtown Baltimore. Investigators say it will take months to determine the cause, and sources familiar with the inquiry say that nothing so far points to track or equipment failure.

Nevertheless, the derailment has become another statistic in a nationwide trend of accidents.

From 1997 through last year, the rail accident rate climbed from 3.5 per million miles of freight and passenger travel to 4.1 per million miles, according to the Federal Railroad Administration.

The figures found that derailments were up more than 21 percent, that collisions had increased by nearly 18 percent, and that signal failures had risen by nearly 80 percent in that period.

Over the same period, the number of hours worked by railroad employees declined by 2.6 percent, Federal Railroad Administration statistics show.

''You've got a very large system that's under heavy pressure that is being staffed by fewer people,'' said Steve Moss of RailWatch, a rail safety advocacy group.

Several serious accidents have occurred recently. In March, Amtrak's California Zephyr derailed in Iowa, killing one passenger and injuring 90. In May, 2000, a Union Pacific train carrying toxic chemicals derailed in Louisiana, forcing the evacuation of 3,000 people from their homes.

The number of accidents involving hazardous materials also increased, from 472 in 1997 to 650 last year, according to federal rail statistics.

''The system is breaking down because it's not being kept up properly, and there's more strain on it,'' Moss said.

The Federal Railroad Administration and railroad companies vehemently disagree.

''The vast majority of the accidents are at the way low end of the scale,'' said the administration's safety director, George Gavalla. ''You don't really see that escalation on the main tracks.''

Most accidents, he said, occur in rail yards and are minor. And although the accident rate might have increased, the number of deaths has dropped 41 percent, he said.

''We're putting our emphasis on where the public risk is, and we're driving down that risk,'' Gavalla said.

He also said that accidents this year are running about 30 percent behind last year's pace. Despite the Baltimore chemical-train derailment, the percentage of rail accidents involving hazardous materials is also down this year.

Still, many observers say that the economics of railroading is changing, with unpredictable consequences for business and safety.

In congressional testimony this spring, transportation analysts depicted a struggling industry starving for revenue and capital to maintain its costly infrastructure of tracks and trains.

Even railroad executives -- while maintaining that tracks, signals, and locomotives are in excellent condition -- acknowledge that competitive pressures have forced them to curtail spending on maintaining and expanding the rail network to handle growing traffic.

Many observers say the increase in accidents in the late 1990s is rooted in the series of major rail combinations that snarled operations and that reflected significant economic pressures on the merged railroads.

CSX and Norfolk Southern agreed in 1997 to pay $10.2 billion to acquire and to divide Philadelphia-based Conrail. The same year, Burlington Northern won a bidding war to buy the Atchison, Topeka, and Santa Fe Railroad. The price was $4.1 billion.

Union Pacific, the loser in the bidding war, then spent about the same amount to buy Southern Pacific Rail Corp. in an effort to stay competitive.

Since then, the number of inspectors and maintenance workers nationally has dropped about 10 percent, according to the Brotherhood of Maintenance of Way Employees, the union that represents those workers.

''Unfortunately, the cost-cutting falls heavy on the maintenance departments,'' said Rick Inclima, safety director for the union.

Concerned about economic effects of the mergers, the Surface Transportation Board, a federal regulatory agency, moved last year to freeze rail combinations.