Updated

Witnesses regularly broke into a sweat at the prospect of testifying before Rep. John Dingell, whose interrogations once made him a feared watchdog on Capitol Hill.

Somewhat muffled by a Republican takeover, the Michigan Democrat celebrates his 50th anniversary in Congress on Tuesday after setting the tone for its investigations from the mid-1970s until the mid-1990s.

"Oversight takes many forms. Congressional investigations, hearings, phone calls, letters," Dingell, 79, said in a recent interview. "And the best part of all is they all involve one thing: Asking questions. Who, what, why, whom and how."

Dingell, who represents a district outside Detroit, is the third-longest serving House member in history. Called "Big John" for his large frame and imposing manner, Dingell has cast more than 21,800 roll call votes, served under 10 presidents and led the House Energy and Commerce Committee.

The son of a congressman, Dingell's work on Capitol Hill predates the lives of many of his colleagues. As a young page, he was on the House floor when President Roosevelt declared war on Japan following the attack on Pearl Harbor.

After the death of his father in 1955, Dingell won a special election to succeed him in Congress. He told his new colleagues: "If I can be half the man my father was, I shall feel I am a great success."

Dingell was one of the most powerful members of the House during the 14 years he chaired its Energy and Commerce Committee, which had the largest staff and budget of any panel in Congress. But it was as chairman of the panel's oversight and investigations subcommittee that he earned his reputation as a pit bull.

During the 1980s and early 1990s, Dingell and his staff pursued investigations into almost everything from the safety of the nation's blood supply to $640 toilet seats purchased by the Defense Department.

"You had to be prepared," said Frank G. Zarb, who testified before Dingell's panel dozens of times as President Ford's senior energy official. "You didn't come in and try to trick your way out of it."

Dingell's subcommittee work led to the firing of the Superfund administrator during the Reagan administration, the discovery of a defense contractor charging the Pentagon for the boarding of a dog and improper billing practices by universities for research expenses.

Dennis Fitzgibbons, a former Dingell aide who directs public policy for DaimlerChrysler AG, remembers the congressman telling evasive witnesses: "That's a very fine answer you've provided. Unfortunately that doesn't match the question I ask."

Norman Ornstein, a resident scholar with the American Enterprise Institute, said Dingell's work in government oversight stands in contrast to "an embarrassing lack of oversight in the last five years" that was exposed by the Federal Emergency Management Agency's slow response to Hurricane Katrina.

"He was fierce in oversight, deeply protective of Congress' prerogatives or powers. He didn't care if it was a Democratic president or Republican president," Ornstein said.

A lifelong outdoorsman, Dingell has been a leading opponent of gun control, to the consternation of many Democrats. He's also been a leading advocate for the auto industry and has been targeted by environmentalists, who have questioned his opposition to strict auto emission standards. "His concern for the environment ends at the car door," said the Sierra Club's Dan Becker.

Dingell points to his environmental record, which includes support for the National Environmental Policy Act, the Endangered Species Act and the Clean Air Act.

"The difference between me and some of my critics on this matter is I understand that both sides have a place in our economy and our society," he said. "There has to be a balance."

His greatest disappointment was the failure of President Clinton's universal health insurance bill. Dingell, like his father, has advocated for universal health care throughout his career.

The House has only two members in its history with longer terms, the late Jamie Whitten, D-Miss., with 53 years, 2 months and 13 days, and the late Carl Vinson, D-Ga., with 50 years, 2 months and 13 days.