Four leading Democratic members of the U.S. House Judiciary Committee on Friday asked the new attorney general and Homeland Security secretary to investigate civil-rights complaints stemming from Maricopa County Sheriff Joe Arpaio's crackdowns on illegal immigration.

The four lawmakers called on Attorney General Eric Holder and Homeland Security Secretary Janet Napolitano to investigate complaints that deputies used skin color as the basis to search for illegal immigrants. They also asked that a federal agreement allowing the Maricopa County Sheriff's Office to enforce immigration laws be terminated if any problems can't be fixed.

The lawmakers are the highest-level officials, and the first under the new Obama administration and Democratic-controlled Congress, to make such a request. They are committee Chairman John Conyers Jr. of Michigan, Zoe Lofgren of California, Jerrold Nadler of New York and Robert Scott of Virginia.

Last year, Phoenix Mayor Phil Gordon, along with civil-liberties and immigrant-advocacy groups, called for similar investigations of Arpaio.

The sheriff on Friday adamantly denied his deputies use racial profiling in arrests of illegal immigrants. "We're doing the right thing," he said. "If I was worried, with all the allegations, why would I keep doing it? I'm not stupid, having worked for the feds for 30 years."

The lawmakers' request, in the form of a letter, comes a few weeks after Napolitano ordered the Department of Homeland Security to conduct a wide-ranging review of immigration enforcement and border security. That includes a review of the federal program, known as 287(g), that gives state and local agencies the authority to enforce immigration laws.

In a memo, Napolitano ordered her staff to study the effectiveness of allowing police to arrest illegal immigrants vs. allowing jailers to identify and hold them when they are arrested for crimes. She also wrote that she wants to see what can be done to speed the process for signing more 287(g) agreements.

Arpaio said this week that he is worried the former Arizona governor will eliminate the provision that allows local police to arrest illegal immigrants.

Legal experts have said Arpaio's practices were likely to get more scrutiny under the Obama administration. Holder has a track record of investigating allegations of racial profiling against police departments when he was deputy attorney general under the Clinton administration. As governor, Napolitano yanked state funding that helped pay for Arpaio's controversial neighborhood sweeps, which critics said were aimed at arresting illegal immigrants.

In Friday's letter, Conyers and the other Democrats said that, in recent months, Arpaio had shown "a blatant disregard for the rights of Hispanic residents in the Phoenix area."

Lofgren is chairwoman of the immigration subcommittee. Nadler is chairman of the Constitution subcommittee, and Scott is chairman of the crime subcommittee.

The lawmakers wrote that Arpaio had apparently overreached his authority under the federal agreement by ordering deputies to "scour Latino neighborhoods" to search for illegal immigrants on the basis of skin color.

"As a result, members of the Latino community - whether they are U.S. citizens or foreign-born, whether they are legal immigrants or undocumented - feel under siege," the letter said.

The Democrats said an incident this month in which Arpaio, citing a need to cut costs, "paraded approximately 200 suspected illegal immigrants in shackles to a segregated area of his Tent City county facility" also warranted investigation.

Arpaio denied his policies are discriminatory toward Latinos and called the 287(g) program "a great success."

"We've done a great job when you look at all the arrests we've made and all the (illegal immigrants) we've found who have been booked into the jail," he said.

Arpaio compared the House members' request to similar ones made in the past year by Gordon and advocacy groups. None resulted in a federal investigation.

Vincent Picard, a spokesman for the Phoenix office of U.S. Immigration and Customs Enforcement, said Arpaio has not violated the 287(g) agreement. The pact prohibits ICE-trained deputies from targeting illegal-immigrant suspects based on race or appearance.

Although allegations of racial profiling are common, not a single firsthand complaint involving ICE-trained officers in Arizona has been filed with the Department of Homeland Security's Office of Inspector General or any other investigative agency, Picard said.

Some legal immigrants have been detained under the program, he said, but in every case, ICE determined they weren't carrying their green cards as required.

"Arizona's 287(g) program is working as intended," Picard said.

Conyers has come under fire from some Democratic lawmakers for pushing too hard for investigations of the Bush administration. Last year, Conyers threatened to file articles of impeachment against President George W. Bush that alleged constitutional violations of civil liberties. But he was discouraged by the Democratic Party leadership.

Rep. Trent Franks, a Republican and the only Arizona member of the House Judiciary Committee, was traveling Friday night and could not be reached for comment.

The Justice Department will review the letter, spokeswoman Laura Sweeney said.

Napolitano has asked for a review of the 287(g) program because of questions about how agreements with state and local agencies are administered and if uniform standards are being applied, said Dean Smith, a Homeland Security spokesman. The review is due next Friday.

Republic reporter JJ Hensley and John Yaukey of Gannett News Service contributed to this article.