WASHINGTON — The Obama administration’s top environmental official in the oil-rich South and Southwest region has resigned after Republicans targeted him over remarks made two years ago when he used the word “crucify” to describe how he would go after companies violating environmental laws.

In a letter to Environmental Protection Agency Administrator Lisa Jackson sent Sunday, Al Armendariz says he regrets his words and stresses that they do not reflect his work as administrator of the five-state region including Texas, New Mexico, Oklahoma, Arkansas and Louisiana. Armendariz, who holds a doctorate in environmental engineering, apologized last week for his remarks. A senior administration official, speaking on condition of anonymity because of the sensitivity of the subject, told The Associated Press that Armendariz has since received death threats. His resignation was effective Monday, when he informed his senior staff. Sam Coleman, a career official who led the agency’s response to Hurricane Katrina and served as Armendariz’ deputy, took over as acting regional administrator.

“I have come to the conclusion that my continued service will distract you and the agency from its important work,” Armendariz wrote in the letter, which was obtained by the AP.  

Republicans in Congress had called for Armendariz’ firing, after Oklahoma Sen. James Inhofe highlighted the May 2010 speech last week as proof of what he refers to as EPA’s assault on energy, particularly the technique of hydraulic fracturing, or fracking.

At a town hall meeting in Washington on Friday, Jackson had said only that she would continue to review the case, calling Armendariz’ words “inflammatory” and “wrong”. President Barack Obama appointed Armendariz in November 2009, at the urging of Texas-based environmental groups. He is one of the few Latinos in senior leadership at the EPA.

The regional administrator’s words “don’t comport with either this administration’s policy on energy, our policy at EPA on environmental enforcement, nor do they comport with our record as well,” Jackson said.

The EPA, perhaps more than any other agency, has found itself in the GOP’s crosshairs over its regulation of the gases blamed for global warming, steps it has taken to limit air pollution from coal-fired power plants, and its increased regulation of fracking, which is responsible for a gas drilling boom. Republicans, including presidential contender Mitt Romney — who has called for Jackson herself to be fired — have blamed the agency for high gasoline prices and clamping down on American energy.

Armendariz, who was based in Texas, frequently found himself at odds with the state government and the oil and gas industry, which are often aligned.

The scientist and environmental activist had long been frustrated by the government’s inability to clean up Texas’ notoriously polluted air, and he had called the EPA broken and testified on behalf of activist groups about just how badly the federal and state environmental agencies had botched things.

Environmentalists said Monday that it was Armendariz getting crucified for doing his job — enforcing the law.

“He took bold steps that have been needed for decades to move our state forward,” said Ken Kramer, director of the Lone Star Chapter of the Sierra Club. “The only people who will celebrate his resignation are the polluters who continue to foul Texas air and the politicians who serve those special interests.”

Several disputed contamination cases in Texas in which Armendariz was involved have helped stoke environmental concerns over fracking, a technique in which oil and gas producers inject water, chemicals and sand underground at high pressures to fracture rock so gas can come out.

In one case cited by Republicans, the EPA issued an emergency order in 2010 — an unprecedented action in Texas — accusing Range Resources of contaminating an aquifer and giving it 48 hours to provide clean drinking water to residents. Armendariz said he went around the state agency that oversees drilling because it wasn’t responding quickly enough. The order later was withdrawn after a state court ruled evidence that fracking had caused the contamination had been falsified.

“He was flat wrong,” wrote more than two dozen lawmakers in a letter to Jackson sent Friday, calling for Armendariz’ firing. “There was no contamination and his office failed to conduct appropriate or adequate science to support his claims.” The EPA has faced similar criticism for its analysis of potential drinking water contamination from fracking in Pennsylvania and Wyoming.

Armendariz’ speech was made in Dish, a small town northwest of Dallas, where residents’ concerns over the environmental impacts of hydraulic fracturing helped put the issue on the national stage.

Testing, which was urged by the EPA, showed some groundwater contamination and elevated toxic air pollution after operators began using a new method — a combination of hydraulic fracturing, or fracking, and horizontal drilling — to extract once out-of-reach gas.

Referring to how the Romans once conquered villages in the Mediterranean, Armendariz said, “They’d go into a little Turkish town somewhere, they’d find the first five guys they saw and they’d crucify them.”

“And so you make examples out of people who are in this case not complying with the law,” he said.” Find people who are not complying with the law and you hit them as hard as you can and make examples of them.”