* Republicans say McCarthy failed to address transparency concerns
* McCarthy answered more than 1,000 written questions from senators
* White House: "historic level of obstructionism" (Adds White House comment)
By Valerie Volcovici and Roberta Rampton
WASHINGTON, May 9 (Reuters) - Republican senators on Thursday stalled the confirmation of President Barack Obama's pick to lead the U.S. Environmental Protection Agency, saying they were "completely unsatisfied" with answers provided by Gina McCarthy on several topics.
Their decision to boycott the Senate Environment Committee meeting on her nomination was the latest in a series of procedural moves by Republicans that have made it difficult for Obama to get his second-term Cabinet in place. Obama has complained that Republicans have stymied his agenda at every turn.
The dispute over McCarthy stems from more than 1,000 written questions Republican senators asked her after her confirmation hearing - what Democrats say is a new record for the number of written questions asked of a nominee.
An administration official said she answered every one.
David Vitter of Louisiana, the top Republican on the Environment Committee, told reporters their boycott was not related to McCarthy's qualifications but to her refusal to answer questions about transparency within the agency.
All eight committee Republicans refused to participate in a scheduled vote on McCarthy, leaving her nomination in limbo and unable to advance to the next stage - a full Senate vote.
The White House responded with outrage. "There has been a historic level of obstructionism from the Senate on this nomination and others," White House spokesman Jay Carney told reporters aboard Air Force One.
Republican senators noted that Environment Committee Democrats, when in the minority, staged a similar boycott in 2003 of EPA nominee Michael Leavitt, forcing a vote to be rescheduled. Leavitt was ultimately confirmed.
It was not immediately clear when the committee would reschedule the vote, which McCarthy is expected to clear, given that Democrats hold a majority on the panel.
Republican Senator Roy Blunt, who is not a member of the Environment Committee, has already said he will put a hold on McCarthy in the full Senate because of delays in approvals for a floodway project in his home state of Missouri.
PAGES OF QUESTIONS
The number of written questions for McCarthy far exceeded those faced by other Cabinet members and previous EPA picks.
Republicans asked Lisa Jackson, Obama's first EPA administrator, 118 questions after her nomination hearing, said a Democratic official familiar with the nomination process.
Jack Lew, now treasury secretary, fielded 462 written questions after his confirmation hearing earlier this year.
"Part of the goal is to wear down and make untenable the nomination," said George Washington University's Sarah Binder, an expert on Congress, who said in an interview that Obama has had a difficult time getting Senate approval for his Cabinet choices compared to previous presidents.
Although the Democratic majority controls the Senate and its committees, congressional rules give some procedural advantages to the minority Republicans enabling them to stall or block legislation and nominees.
The boycott of McCarthy's vote comes a day after Republican senators used an obscure procedural rule to delay a scheduled committee vote on Obama's nominee for labor secretary, Thomas Perez.
The nomination of Ernest Moniz, Obama's pick to head the Energy Department, has also stalled over a dispute with a South Carolina senator about the government's management of a nuclear waste disposal project in the state.
Earlier this year, Defense Secretary Chuck Hagel and Central Intelligence Agency Director John Brennan also had tough work getting Senate confirmation.
AGGRESSIVE EPA RULES
In his first term, Obama aggressively used EPA authority to try to cut pollution, although the White House ultimately killed a rule that would have regulated ozone levels because it would have cost too much.
Republicans have argued that various EPA rules have hurt jobs, and the coal industry in particular, and have accused the agency of not being transparent in its policies, including in the way it handles internal communications, the use of personal emails and the way it uses data in EPA rulemaking.
McCarthy was in charge of developing many of those regulations in her previous job at the EPA. She is well-known among lawmakers, and industry groups regulated by the EPA, including the American Petroleum Institute backed her nomination when it was announced. The API had no immediate comment on Thursday's actions.
McCarthy was a state environmental official in Connecticut and Massachusetts before joining the EPA in 2009 as assistant administrator of the Office of Air and Radiation. She sailed through the Senate nomination process for that role. She was the top environmental enforcer for Mitt Romney, the 2012 Republican presidential nominee, when he was governor of Massachusetts.
Environmental groups called the Republican tactics "new lows" given her qualifications and popularity.
"By any measure, Gina McCarthy deserves to be confirmed, but Republicans on this committee are apparently more concerned with scoring political points than protecting public health," said Gene Karpinski, president of the League of Conservation Voters.
Democratic Senator Tom Carper of Delaware said McCarthy had gone "above and beyond the requirements of a nominee" in answering more than 1,000 questions and meeting with almost half the 100-member Senate.
Wyoming Republican John Barrasso said the delay in McCarthy's nomination would not pose an operational problem for the agency, calling acting administrator Bob Perciasepe was "more than qualified" to run the EPA in the meantime. (Reporting by Valerie Volcovici and Roberta Rampton; additional reporting by Rachelle Younglai; writing by Ros Krasny; editing by Vicki Allen and Jackie Frank)
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