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

That timing is no coincidence, safety advocates, economists and union leaders say. Maintenance has suffered, they contend, 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.

No one can say what role, if any, track conditions played in the derailment July 18 of a 60-car CSX train carrying hazardous chemicals through the Howard Street Tunnel. 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 one more statistic in a nationwide trend of increasing accidents.

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

The figures show derailments up more than 21 percent, collisions up nearly 18 percent and signal failures up nearly 80 percent during that time. Over the same period, the number of hours worked by railroad employees declined by 2.6 percent, FRA 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 national rail safety advocacy group.

Several serious rail accidents have occurred recently. In March, Amtrak's California Zephyr derailed in Iowa, killing one passenger and injuring 90. Last year, 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 rose, from 472 in 1997 to 650 last year, according to federal rail statistics.

'More strain'

"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 FRA Safety Director George Gavalla. "You don't really see that escalation [of accidents] on the main tracks."

Most of the accidents, he said, occur in rail yards and are minor. And although the overall accident rate might have increased, the number of fatalities 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.

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 contend that economics is changing the nature of railroading, with unpredictable consequences for business and safety.

In congressional testimony this spring, transportation analysts depicted a struggling industry that is 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.