WASHINGTON -- A quartet of senators yesterday leveled a barrage of questions at federal mine regulators about their handling of a West Virginia coal mine where an explosion killed 12 workers this month.

The chairman of the Senate subcommittee, Arlen Specter, R-Pa., later suggested he might issue subpoenas after the head of the Mine Safety and Health Administration walked out after he was requested to stay and take further questions.

David G. Dye, acting assistant secretary of labor for mine safety and health, defended the Bush administration's record on mine safety, citing an uptick in enforcement actions in the past five years.

He also said the administration was committed to more than tripling the statutory limit on fines for mine safety violations from its current $60,000 to $220,000.

Mr. Dye and his chief deputy for coal mine safety, Ray McKinney, received tart questioning from Mr. Specter and Sens. Robert Byrd, D-W.Va., Tom Harkin, D-Iowa, and Michael DeWine, R-Ohio.

The senators, members of the Appropriations Subcommittee on Labor, Health and Human Services, Education and Related Agencies, held more than two hours of hearings into the Sago mine disaster in Tallmansville, W.Va.

Mr. Byrd pointedly asked Mr. Dye if "cronyism" between MSHA and coal industry officials had affected the quality of safety enforcement.

"There's no cronyism between me and anyone in the industry," Mr. Dye replied, adding that MSHA field inspectors "have a fire in their belly to go out and protect miners."

Some of the harshest questioning came from Mr. Byrd, who requested yesterday's hearings.

"We must try to determine what is wrong at MSHA, and contemplate how to make sure the leadership of that agency does its job," Mr. Byrd said in his opening statement.

Senators quizzed Mr. Dye on why coal mines have not made regular use of positioning equipment that allows them to locate miners, communications setups that would send evacuation and rescue notices, and state-of-the-art air supply technology that would give miners and rescue teams more than one hour of oxygen.

Mr. Harkin, ranking Democrat on the subcommittee, displayed a text message system that is worn by underground miners in Australia. J. Davitt McAteer, who is heading up the state of West Virginia's investigation into Sago, displayed a pager-size transponder that gives a miner's position underground.

Bennett Hatfield, president of International Coal Group, owners of the Sago mine, said the devices have some technical difficulties, but that the company is committed to employing them at its mines in the future.

Mr. Dye had earlier said such devices were not reliable for underground coal mining, but Mr. McAteer challenged that assertion. By then, Mr. Dye was out of the room.

"These devices have been approved by the Mine Safety and Health Administration," Mr. McAteer said. "I must disagree with the secretary." These devices have been proved to be reliable. He estimated the top cost to install a tracking system in a mine the size of Sago, where 145 people are employed, at $100,000.

The display of new technology was bracketed by harsh words from both Democrats and Republicans on the panel. Mr. Specter demanded to know if any of the 208 federal citations issued against Sago last year was "a causative factor for this disaster."

"We're still investigating," said Mr. McKinney.

Mr. Specter focused on budget cuts at MSHA, which he said resulted in 183 eliminated positions. He asked if those staff reductions affected enforcement quality.

"No, I don't think so," Mr. Dye responded.

Mr. Byrd demanded to know why it took two hours for MSHA to be notified of the explosion at Sago Jan. 2.

"We don't have that answer yet," Mr. Dye said. "That's one of the things we're going to be investigating."

"I think as secretary you should know the answer now," Mr. Byrd replied. "Why did it take two hours for MSHA to be notified? Then, why did it take six hours for the rescue teams to arrive? Why was a rapid notification and response not available? Shouldn't that mine have been closed with all those citations, all the breaking down and tearing down and easing of the regulations? Why?"

When Mr. Specter asked Mr. Dye to remain for the second hour of the hearing to deal with questions that might be raised by the next group of witnesses -- including officials of ICG, the state and national coal associations, Mr. McAteer and Cecil Roberts, president of the United Mine Workers -- he said the weekend deaths of two miners at the Alma mine in southern West Virginia and a fire in Colorado required his attention.

"We have really urgent matters that we've got to go back to," Mr. Dye said. "We really need to get back to attend to all this."

"It may well be that some of the other senators here have pressing matters, too," Mr. Specter replied. "We don't think we're imposing too much to keep you here for another hour. That's the committee's request. You're not under subpoena."

As other panelists took their seats, Mr. Dye and Mr. McKinney slipped out a back door. A Labor Department spokesman, Dirk Fillpot, said the men had "scheduling pressures" that required them to leave.

The departure drew Mr. Specter's attention after the next panel had spoken and he pointedly said he had hoped to ask Mr. Dye if he had any ambitions of rising in the MSHA ranks. Outside the hearing room, Mr. Specter hinted that while the MSHA officials were not under subpoena today, they might yet be.

"I told them they weren't under subpoena deliberately, so they would understand that they were going to have to stay as a matter of compliance with a subcommittee request," Mr. Specter said. "I know how to issue subpoenas and I've got a large supply. I may issue some yet for those two gentlemen."

Mr. Hatfield, president of ICG, which took over management of Sago in the middle of last year from the former Anker West Virginia Mining Co., answered questions from the senators, pledged major investments in technology and tentatively endorsed Mr. Dye's suggestion for increasing safety violation fines.

Despite assertions it has made millions of dollars in safety improvements in its mines, including the upgraded intake airway through which a crew of miners escaped to safety the morning of the accident, International Coal Group has faced questions about its handling of Sago.

Senators asked about the delay in notifying MSHA and deploying rescue crews, as well as the miscommunication that initially led company officials, as well as families of the trapped miners, to believe that 12 of the 13 had survived, when in fact only one, Randal McCloy, remained alive.