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Several Republican lawmakers are challenging the Obama administration's science czar over what they claim are repeat incidents of "scientific misconduct" among agencies, questioning whether officials who deal with everything from endangered species to nuclear waste are using "sound science."

The letter sent Wednesday to John Holdren, director of the Office of Science and Technology Policy, cited four specific controversies in recent years where scientific findings were questioned. Sens. David Vitter, R-La., and James Inhofe, R-Okla., and Rep. Darrell Issa, R-Calif., rattled off a slew of questions on what they called "the apparent collapse in the quality of scientific work being conducted at our federal agencies."

"Specifically, we are concerned with data quality, integrity of methodologies and collection of information, agencies misrepresenting publicly the weight of scientific 'facts,' indefensible representations of scientific conclusions before our federal court system, and our fundamental notions of 'sound' science," they wrote. "We identify in this letter important examples of agency scientific misconduct."

Inhofe spokesman Matt Dempsey told FoxNews.com the issues in the letter had been on Republicans' radar screen "for some time." But he said the lawmakers decided to compile them and confront the administration about it out of concern that a "trend" was developing.

"The concern is there's a lot more there," he said.

White House representatives so far have not returned requests for comment on the letter.

The Republicans' letter cycles through several incidents the lawmakers claim to be troubling.

One concerned the controversy over a temporary deepwater drilling moratorium was issued in May 2010. In the announcement, the Interior Department said the report's recommendations had been "peer-reviewed" by experts with the National Academy of Engineering. But those experts later complained, saying the moratorium was not among their approved recommendations -- this led to an apology from Interior Secretary Ken Salazar.

Interior officials later told the inspector general's office probing the incident they did not intend to imply those experts supported the drilling ban.

The GOP lawmakers, though, said the incident shows "blatant political influence" in the decision making.

The lawmakers also questioned an EPA assessment on the dangers posed by formaldehyde -- the National Research Council earlier this year claimed the assessment did not adequately back up some of its claims, including claims that the chemical causes leukemia and respiratory tract cancers.

In another case, the lawmakers highlighted the scolding a federal judge gave the Fish and Wildlife Service last month over testimony in defense of a plan to protect a tiny fish called delta smelt by diverting water in California away from farmland. U.S. District Judge Oliver Wanger said the testimony was "riddled with inconsistency."

In their letter, the lawmakers focused most on concerns about the 2009 decision to pull the plug on the controversial Yucca Mountain nuclear waste site in Nevada. The project years in the making faced heavy opposition in Nevada.

Energy Secretary Steven Chu in 2009 said the project was simply not a "workable option." In early 2010, the department withdrew its license application for the site, and moved instead to impanel a commission to look at alternative sites. A department filing at the time noted that scientific knowledge on nuclear waste had "advanced dramatically" in the 20 years since the project started.

But the Government Accountability Office said in an April report the DOE did not cite "technical or safety issues" in its decision.

"Amid uncertainty over whether it had the authority to terminate the Yucca Mountain repository program, DOE terminated the program without formally assessing the risks stemming from the shutdown, including the possibility that it might have to resume the repository effort," the report said.

A June report from Republicans on the House Science, Space and Technology Committee also said the panel could not find a "single document" to support claims that Yucca Mountain is unsafe for nuclear waste.

Not all Republicans are united in backing the Yucca site, however.

It's a sensitive issue in Nevada, and at the Republican presidential debate in Las Vegas Tuesday night top GOP candidates said the federal government should not be sticking Nevada with the waste.

"The idea that 49 states can tell Nevada, 'We want to give you our nuclear waste,' doesn't make a lot of sense," former Massachusetts Gov. Mitt Romney said.

For the incidents cited in the letter to Holdren, the lawmakers asked for more information about how the alleged missteps occurred and what the administration intends to do about them.

Though Inhofe is best known on the scientific front for challenging climate change science and the regulations that emerge from it, the letter did not specifically address climate change.

But in a separate letter, the Competitive Enterprise Institute on Tuesday sent a Freedom of Information Act request to Holdren's office asking for records on coordination between his office and the United Nations climate change panel.

In a statement, the group charged that a U.N. plan would "hide" online correspondence by using non-governmental accounts. CEI urged the White House to use official email channels.