The independent watchdog for the National Archives and Records Administration is entering his 18th month on paid time off following allegations of professional misconduct, a case that has cost taxpayers $377,000 in his salary and legal fees paid by the government.

Inspector General Paul Brachfeld ’s long span on paid administrative leave while his case is investigated prompted three senior Republicans in Congress last week to rebuke the archivist of the United States, Brachfeld’s boss and the official who placed him on leave.

In a stinging letter , the lawmakers told David Ferriero that by allowing the case to drag on, he has wasted taxpayer money, compromised the watchdog mission of the inspector general’s office and called his own leadership into question.

“The failure to resolve this matter in a timely way threatens the independence of IGs and frankly raises questions about your leadership,” wrote Sen. Charles E. Grassley (Iowa), ranking Republican on the Senate Judiciary Committee; Sen. Tom A. Coburn (Okla.), the ranking Republican on the Senate Homeland Security and Governmental Affairs Committee; and Darrell Issa (R-Calif.), chairman of the House Oversight and Government Reform Committee.

Brachfeld, 56, a career civil servant, was placed on leave Sept. 14, 2012 after an agent on his staff with whom he had clashed filed a complaint with two federal offices that investigate claims of government wrongdoing. A handful of other employees in the inspector general’s office also filed complaints.

They included allegations that Brachfeld altered audits; provided sensitive law enforcement information to reporters for CBS News’s “60 Minutes” before law enforcement officials had approved its release; made derisive comments about transgender people; had a security guard fired because of his race; and used vulgar language with some female staff members.

Brachfeld has denied the allegations. A review by the Office of Special Counsel concluded a year ago that he did not violate any personnel practices that are prohibited by the government. The other inquiry, by the Council of the Inspectors General on Integrity and Efficiency , is drawing to a close, said several law enforcement and congressional sources with knowledge of the investigation.

“I have every confidence I’ll be cleared,” Brachfeld said in an interview. “I never dreamed the case would go on this long.”

By sidelining Brachfeld for so long with a “seemingly unlawful imposition” of extended paid leave, the archivist has “decapitated the office that Congress established to be the taxpayers’ watchdog of your agency,” the lawmakers wrote in their five-page letter Friday.

Ferriero did not respond to several e-mails seeking comment. Archives spokesman Chris Isleib declined to comment on specifics of the case, saying that agency personnel matters are not public. Isleib noted that the matter is under review by the panel that investigates complaints against inspectors general, “a process whose timing National Archives does not control,” he said in an e-mail.

In a letter in August addressing the lawmakers’ concerns about the lengthy leave, Ferriero wrote that he “bears no animus towards Mr. Brachfeld.”

“I am aware the length of his leave is frustrating to all involved,” the archivist wrote, “but I do not control the schedule and timeliness of the outside investigations that, in my judgment, warrant keeping him on leave.”

The case has highlighted concerns about due process for inspectors general, whose role as government watchdogs combating waste, fraud and abuse requires them to be independent. At large federal agencies, the nominees for the position are confirmed by the Senate; at smaller agencies that include the Archives, inspectors general are hired and can be fired by the head of the agency.

The situation has brought to light federal agencies’ common practice of placing employees on paid leave when they are accused of breaking rules. The leave can go on for months and even years. Brachfeld, who lives in Silver Spring, has received his full senior executive salary of $187,000 with benefits, vacation and pension contributions by the government. Ferriero hired an outside law firm to handle the case; the firm has been paid $129,000 to date.

His case has prompted the Government Accountability Office to review the government’s use of paid administrative leave and whether it is abused. The GAO, Congress’s investigative arm, is looking at the frequency, duration and “associated salary cost” of this kind of time off, according to a Jan. 31 document laying out the terms of work.

Brachfeld has had a long government career that includes high-level auditing positions with the Treasury Department, the Federal Election Commission, the former U.S. Customs Service and the Federal Communications Commission. Since becoming the inspector general of the Archives in 2000, he has built a reputation as a hard-charging, creative watchdog over the agency responsible for preserving historical records.

He also enjoys the limelight and has sought to bring publicity to the work of his office, which has rankled some colleagues.

When Ferriero placed Brachfeld on leave, he referred the allegations to the special counsel’s office and the inspector general council, which said it would wait for the special counsel to complete its work. The special counsel cleared Brachfeld of the allegations of prohibited personnel practices but said other allegations were beyond its purview. Ferriero resubmitted the case to the inspector general council a year ago, congressional and government sources said.

Complicating the case, the council meets just four times a year, a system that critics say denies due process to those under investigation. Brachfeld said he was not interviewed until last week.

Christopher Allen, a spokesman for the council, declined to comment.

Federal law does not explicitly authorize paid administrative leave. But agencies have discretion to grant excused absences for 64 activities, including donating blood as well as attending a Boy Scout or Girl Scout jamboree. Among those activities are investigations of misconduct.

But that discretion is supposed to apply for short periods. The lawmakers told Ferriero that he may have broken federal policy by keeping Brachfeld on leave for so long.

The inspector general’s office has been led in Brachfeld’s absence by an acting director. Brachfeld said Ferriero has instructed him not to contact anyone on his staff while he is under investigation.

Brachfeld is eligible to retire from the government. But he said that on principle he will not.

“I was a highly effective and highly rated inspector general,” he said. “I will not retire until I am cleared and my good name is restored.”