“Data shows that releases from pipelines have declined over the last decade as the result of stringent regulation and the industry’s continued commitment to safety,” wrote Peter Lidiak, pipeline director for the American Petroleum Institute, an industry group, in an e-mailed response.

Throwing more resources and money at the problem may not be the answer for the tiny agency, because there remain deeper concerns about how it works, especially its reluctance to mandate safety improvements or to level meaningful fines for wrongdoing.

Such concerns come at a critical time for the agency. The State Department last month gave a provisional green light to a controversial 1,661-mile pipeline from Canada to Texas, called Keystone XL, that will carry a trickier form of crude — and fall under the agency’s purview. And a just-released National Transportation Safety Board report on a natural gas pipeline explosion in San Bruno, Calif., that last year cost eight people their lives, characterized the agency’s regulatory practices as lax and inadequate. In the report, the safety board urged the Transportation Department to go back and audit many of the pipeline agency’s safety and enforcement policies.

An analysis of federal reports and safety documents by The New York Times suggests that while the agency performs better than it did 10 years ago, it still struggles to safeguard a transport network laced with risks.

For example, the agency requires companies to focus their inspections on only the 44 percent of the nation’s land-based liquid pipelines that could affect high consequence areas — those near population centers or considered environmentally delicate — which leaves thousands of miles of lines loosely regulated and operating essentially on the honor system. Meanwhile, budget limits and attrition have left the agency with 118 inspectors — 17 shy of what federal law authorizes.

Pipeline operators, critics argue, have too much autonomy over their lines, and too much wiggle room when it comes to carrying out important safeguards, like whether to install costly but crucial automated shut-off valves.

“The system as it presently exists, I don’t think it really protects the public,” said Representative Corrine Brown of Florida, the ranking Democrat on the House transportation subcommittee on railroads, pipelines and hazardous materials. “Self-reporting doesn’t work. We need additional rules and regulations to make sure we’re doing what we’re supposed to be doing to protect communities.”