In his first appearance before Congress Thursday, NASA Inspector General Robert W. Cobb was told by lawmakers from both chambers to resign, but he said he would not.

Lawmakers have called for his resignation before, but this was the first time they did so in person. Members of a joint House-Senate committee spent several hours grilling Cobb, who, according to an oversight panel, tried to silence whistleblowers at NASA and regularly subjected his staff to verbal beratement.

“The committees of the House and Senate that are responsible for oversight of NASA are sitting before you. All of us have called upon the president to fire you. Mr. Cobb, you must leave,” said Rep. Brad Miller, D-N.C. “Congress does not trust you. You must leave to preserve what is left of the integrity of your office.”

The President’s Council on Integrity and Efficiency (PCIE), which oversees all federal inspectors general, concluded that although Cobb had committed no crime, he had abused his authority.

But Cobb said the investigation is largely baseless, since the allegations it investigated are false. He also questioned whether the agency has the authority to make such a judgment.

“If the findings of the integrity committee are falsely based, then I don’t see any problem with continuing to serve under those circumstances,” Cobb said. He also suggested that he is staying as a way to fight back against unfair treatment by the government.

Sen. Bill Nelson, D-Fla., said that under Cobb’s leadership, the inspector general’s office has “become dysfunctional. Fear and mistrust permeate the office. More than half of the experienced professionals in the office have left since Mr. Cobb’s arrival.” Nelson also called for his resignation.

Cobb struck back at Nelson, hinting that the senator’s office had a vendetta against him. The PCIE investigation was begun in part due to constituent complaints that Nelson forwarded to NASA and others.

“You have sought investigation of me for more than two years now,” Cobb said, adding that it has been a costly exercise.

Nelson answered that his office had merely forwarded constituent complaints, adding that “one of the roles of an elected official is when constituents complain, to have those complaints referred to the proper authorities.”

Though he did not appear at the joint hearing — held by the Senate Commerce Subcommittee on Space, Aeronautics and Related Sciences and the House Science and Technology Subcommittee on Investigations and Oversight — Sen. Charles E. Grassley, R-Iowa, issued a letter highly critical of Cobb’s performance.

“It seems that Mr. Cobb may care more about protecting NASA from embarrassment than he does about performing the critical functions of his office,” Grassley wrote. Rep. Bart Gordon, D-Tenn., and Sen. Claire McCaskill, D-Mo., also joined the call for Cobb’s resignation, with McCaskill vowing to actively work to gather more support from her colleagues for his removal.

Though Congress has no formal role in determining Cobb’s employment status, lawmakers can exert pressure on the Bush administration to remove him.