Lawmakers on Friday asked the U.S. Department of Justice inspector general to launch an investigation into an undercover federal sting operation in Milwaukee that was marred by a series of missteps and failures.

The letter was written by U.S. Reps. Jim Sensenbrenner (R-Wis.) and Bob Goodlatte (R-Va.), who is chairman of the House Judiciary Committee, and asks the inspector general, an independent entity within the Justice Department, to do its own investigation.

The letter comes a day after the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives failed to meet a deadline to respond to questions from an earlier letter from members of Congress to Acting Director Todd Jones. Members of both parties in Congress are demanding answers about what U.S. Sen. Tammy Baldwin (D- Wis.) has termed a "failed operation."

A Journal Sentinel investigation revealed problems in a 10-month ATF sting in Milwaukee - agents' guns, including a machine gun, being stolen; the loss of an ATF ballistic shield; the theft of nearly $40,000 in merchandise from the sting storefront; careless handling of a sensitive operational plan; and the charging of the wrong suspects.

The ATF's machine gun - stolen from an agent's SUV just weeks before the storefront burglary - remains on the street.

"This undercover operation was botched by a series of embarrassing failures and demands a thorough analysis," the letter says.

While the operation resulted in charges against about 30 people, most were on minor drug and gun counts. However, federal officials note a few of the defendants face long prison terms. The investigation remains open, officials have said.

The ATF has launched an internal "top to bottom" review of the operation, according to an agency spokesman.

The House Committee on Oversight and Government Reform has orally requested that the inspector general open an investigation, said Becca Watkins, spokeswoman for the committee and chairman U.S. Rep. Darrell Issa (R-Calif.).

Issa signed a letter, with Sensenbrenner, Goodlatte and U.S. Sen. Chuck Grassley (R-Iowa) demanding the ATF answer 27 questions about the operation in Milwaukee and others like it. Watkins said ATF officials contacted Issa to say they are investigating and will not be providing a response "in the near future."

ATF spokesman Mike Campbell said the agency is compiling a response to the congressional letters received about the Milwaukee operation, but he could not estimate when responses would be provided.

"We are putting together a report responding to all the questions Congress has given us and we are answering those questions to everyone's satisfaction," he said. "With all the attention this case has received, we are doing this with extreme due diligence."

A spokesman for the inspector general's office said Friday he could not comment.

The office has investigated the ATF for lost or stolen items before. Its investigation found 76 ATF weapons were stolen, lost or missing in a five-year span from 2002-'07, according to the report. That's nearly double the number compared with the FBI and the U.S. Drug Enforcement Administration, when considering rates per 1,000 agents.

In their letter Friday, Sensenbrenner and Goodlatte reminded the inspector general of that report, which also found that the ATF lost a high number of laptop computers. It also reported "serious deficiencies" in how the ATF responded to the lost or stolen items. The letter from Sensenbrenner and Goodlatte said the congressmen were pleased the ATF has launched an internal investigation, but "we believe an independent analysis is needed to shed light on the ATF's handling of this incident."

They said they were particularly concerned in light of the ATF's flawed Fast and Furious operation in Arizona, where agents encouraged the sale of more than 2,000 firearms to traffickers by gun stores but lost track of many of the weapons. Many ended up at crime scenes in Mexico.

Separately, U.S. Sen. Ron Johnson (R-Wis.) is waiting for a response on a letter to Jones expressing concern about the way the operation was handled and anger at how agents treated the owner of the building where they located their undercover storefront. Johnson said he contacted the agency more than two weeks ago after learning about the damage to property but never heard back. David Salkin, the landlord, has said the ATF owes him about $15,000 because of damage to his building, unpaid utility bills and lost rent.

U.S. Rep. Gwen Moore (D-Wis.), who earlier said the sting appeared to be well-intentioned but ultimately was a "failed operation," is waiting to meet with the acting ATF director, said Nicole Williams, spokeswoman for Moore.

Baldwin also wrote a letter asking how the agency chose the city's Riverwest neighborhood where the operation was located. Residents, who learned of the operation from the Journal Sentinel, said they were angry the ATF brought drug dealers and gun-carrying felons to their neighborhood.

Milwaukee Ald. Nik Kovac, who represents the neighborhood where the operation was set up, said he met Friday with U.S. Attorney James Santelle and Milwaukee police earlier in the week. He said he has yet to hear from the ATF.

Kovac said he remains concerned about mistakes made in the case but is reserving judgment until he knows all the "rewards" of the operation - in other words all charges filed, including any yet to come.

"They made a lot of mistakes and put people in Riverwest in danger, and that's unacceptable. But I'm still in the dark in terms of the full accounting, I don't know all the rewards," he said. "Given the high priority of getting illegal guns off the street, I'm glad the federal government is making it a priority in our hometown. I'm angry they screwed up."