Thomas M. Roberts vowed yesterday to remain on the Nuclear Regulatory Commission, dismissing a charge of malfeasance as "ludicrous."

"I continue to respect and honor the public trust that has been placed in me. I vote my mind and my principles without regard to political repercussions or recriminations. I have done nothing to warrant my resignation," Roberts said in a letter to Rep. Sam Gejdenson (D-Conn.).

Gejdenson, chairman of the House Interior and Insular Affairs subcommittee on general oversight and investigations, wrote President Reagan on Thursday urging him to fire the NRC official. He said Roberts improperly met with David H. Martin, director of the Office of Government Ethics, in an attempt to influence an investigation of the chief of the Tennessee Valley Authority's nuclear power program.

Roberts said in his letter that the meeting was "wholly aboveboard and appropriate."

"I did not appear before Mr. Martin as an advocate. Rather, both as a citizen and a potential nominee to a post at TVA, my primary interest . . . was to make sure that the Tennessee Valley Authority ran a clean shop," the commissioner wrote. "To suggest that my purpose was to interfere with the investigation or to intimidate Mr. Martin is, with all due respect, ludicrous."

Responding to another charge, Roberts acknowledged that he met with the defense counsel for a utility under criminal investigation despite a request by federal prosecutors that he inform them before any such meetings were held so they could send a representative.

The U.S. attorney, Roberts said, "of course has no authority over my conduct as a fact witness."