For the second time in as many days, Republicans in the Senate blocked committee action to confirm a nominee to President Obama’s second-term Cabinet, this time by boycotting a Thursday vote on his pick to head the Environmental Protection Agency.

All eight Republican members of the Committee on Environment and Public Works did not appear for a vote that would likely have moved nominee Gina McCarthy’s selection to the full Senate. The senators said she had refused to answer their questions about transparency in the agency.

The Obama administration expressed outrage, describing the boycott as part of a pattern of Republican obstruction to undermine the president’s ability to fill key Cabinet positions.

In the weeks-long hearing on her nomination, McCarthy took more than 1,100 questions, more than 1,075 of which came from Republicans. A single conservative, Sen. David Vitter (R-La.), asked 600 of them, according to the majority office of the committee.

By contrast, the EPA’s former administrator under Obama, Lisa P. Jackson, took 157 questions, 118 from Republicans. President George W. Bush’s nominees to lead the agency, Stephen L. Johnson and Michael O. Leavitt, took 230 and 305 questions, respectively, according to a Democratic official who spoke on the condition of anonymity because the nomination was still pending.

Republicans on the committee caught Democrats unaware, notifying them of the boycott half an hour before the hearing.

Under Senate rules, a committee can vote on a nominee if 10 members constituting a majority confirm that they will be present and vote in the affirmative, a committee spokesman said. Democrats hold a 10-to-8 majority on the panel. A vote will be rescheduled soon with all 10 Democrats present, the spokesman said.

On Wednesday, a confirmation vote on Thomas Perez’s nomination for labor secretary was postponed amid GOP threats to invoke an obscure procedural rule that would have prevented the Senate Health, Education, Labor and Pensions Committee from meeting.

“We call on Republicans in the Senate to stop gumming up the works when it comes to the confirmation process of nominees who are enormously qualified for the jobs that the president has asked them to fill, and to get about the business of confirming them,” White House press secretary Jay Carney said.

In a statement, the Republicans explained the reason for their absence. “The new nominee to be EPA Administrator has been extremely unresponsive with the information we requested,” said Sen. John Barrasso (R-Wyo.).

“We’re not asking to amend any bedrock environmental laws. We’re asking for access to the scientific data and reasoning behind the justification for expensive new rules and regulations that continue to cause high unemployment,” he said.

Republicans in the Senate and House fought the EPA’s attempts under Obama to regulate emissions from power plants and factories and to use the Clean Water Act to limit the pollution allowed to flow into waters such as the Chesapeake Bay.

Conservatives said the regulations reduced profits and cost jobs, a claim that Jackson repeatedly denied, arguing further that the emissions’ greenhouse gases greatly contribute to global warming and that their fine particles lead to respiratory illness and premature death. Water contamination from farms, sewers and industry threaten drinking water, she said.

Democrats on the committee criticized the Republicans’ tactics.

“We know they don’t want answers to questions,” said Sen. Tom Udall (D-N.M.). “They just haven’t showed up.”

Chairwoman Barbara Boxer (D-Calif.) had more pointed remarks. “The bottom line is they’ve gotten answers to their questions, folks. They don’t like the answers. . . . They are holding Gina McCarthy hostage to their polluter-fringe philosophy.”

Some Democrats described Republican obstruction of Obama as unprecedented, but a Republican on the committee said it was nothing new, recalling Boxer’s boycott of Leavitt.

“Back then as chairman, I respectfully delayed the vote,” said Sen. James M. Inhofe (R-Okla.). “Today, Chairwoman Boxer returned that courtesy and decided to give the nominee additional time to respond to the concerns of the minority members.”