The top executive of Massey Energy told a Senate subcommittee Thursday that an outside agency should investigate the April 5 explosion at his company’s Upper Big Branch mine, which killed 29, because otherwise the Mine Safety and Health Administration, the agency now in charge, would have to evaluate its own performance.

In his first testimony since the accident, the worst coal mine disaster in 40 years, Don L. Blankenship, the chairman and chief executive, came out swinging. The 23 miner fatalities at Massey mines in the decade before the Upper Big Branch explosion made his company “about average,” he said, and Massey was a leader in safety innovation but had been forbidden by the Mine Safety and Health administration from making some safety improvements.

Mr. Blankenship spoke at a hearing of the Senate Appropriations subcommittee on labor, health and human services. Senator Tom Harkin, Democrat of Iowa, the chairman, said the hearing would not focus on the details of the accident, because that is part of a separate investigation, but on the backlog of safety cases at the regulatory agency. Massey could have drawn extra scrutiny from the safety agency if it were found to have a “pattern of violations,” but it contested so many citations that it escaped that category.

In fact, the government program for closing unsafe coal mines has defeated itself because the safety agency has added inspectors faster than it has increased the number of judges to adjudicate cases, officials testified on Thursday.

In the 2008 fiscal year, 72 percent of cases were decided within one year. But as of April 30 of this year, only 25 percent of the cases resolved were under a year old, and 62 percent were one to two years old, according to Mary Lu Jordan, chairman of the Federal Mine Safety and Health Review Commission. The government recently added four judges to the 10 it had, but the backlog will grow by the end of this year to 18,200 cases from about 16,000 now.

Senator Harkin said, “There seems to be every incentive to an operator challenge just about every citation.” He promised more money.

Witnesses suggested various changes, including requiring companies to pay interest on fines from the day the fine was proposed if they engage in lengthy appeals and eventually lose the cases.

At the hearing, another witness, Cecil E. Roberts, president of the United Mine Workers of America, challenged Mr. Blankenship’s assertion that Massey’s safety record was average.

“I can’t come up with another coal company that’s had 23 miners in 10 years die,” Mr. Roberts, seated next to Mr. Blankenship at the witness table, said. “This isn’t average. This is deplorable.

“This is the worst fatality rate in the industry either way you look at it, either before the explosion or after the explosion.”

Mr. Blankenship said that given the mining conditions in Massey’s region, central Appalachia, and the volume it produces, numbers “tend to get big,” but he added that any fatality was “unacceptable to us.”

The agency’s prime witness, Joseph A. Main, assistant secretary of labor, did not address how the investigation would be conducted. He said his agency was trying to become more effective, with new tactics like “blitz” inspection raids.

Robert C. Byrd, the 92-year-old West Virginia Democrat, took a tough stance with Mr. Blankenship.

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