Whistle blowers may be a nuisance, but hassling them can cost money. The Nuclear Regulatory Commission is fining the Tennessee Valley Authority $150,000 for harassing three engineers who stood up for a colleague who spoke out about nuclear power plant problems.

The fine is the first against the federal utility for harassing whistle blower employes, according to NRC spokesman Joe Gilliland. However, TVA has amassed $1.3 million in NRC penalties regarding other matters since 1980.

"We anticipate paying the fine, pending an evaluation of the NRC's findings," said TVA spokesman Carl Crawford. "We've not received the actual documentation yet, but we're inclined to pay without appeal."

Nuclear engineers Lillard Blevins, Stephan Mindel and John French were harassed by their supervisors after they defended William Dan DeFord, a fellow TVA engineer who had called attention to quality assurance problems in TVA's nuclear engineering division, officials said.

"The three were treated unfairly in job assignments and performance appraisals and they were not selected for promotion during a reorganization of the TVA office of quality assurance in November 1982," James M. Taylor, director of the NRC office of inspection and enforcement, said in a letter to TVA. Bartholomew to Spain . . .

Reginald Bartholomew, the U.S. ambassador to Lebanon since 1983, will be nominated by President Reagan to be ambassador to Spain.

Bartholomew, a career member of the Foreign Service who served a two-year stint on the National Security Council during the Carter administration, will succeed Thomas O. Enders in Madrid. Enders is leaving government to join the New York investment banking house Salomon Bros. Inc. Legal Briefs . . .

Two new associate counsels to the president have been appointed by the White House. They are J. Michael Shepherd, a deputy assistant attorney general in the Justice Department's office of legal counsel since 1984, and C. Dean McGrath Jr., an attorney in the Treasury Department general counsel's office since 1979. Services to Service . . .

Jane Kenny, an official of the General Services Administration, has been named director of Volunteers in Service to America (VISTA).

Kenny was named to oversee the activities of nearly 2,500 VISTA volunteers. She also will head the National Center for Service-Learning, a nationwide program that assists high school and college volunteer projects.

Kenny was a special assistant to Vice President Bush. Two Hats at Treasury . . .

Reagan plans to nominate William Nelson as assistant general counsel in the Treasury Department, White House officials say.

Nelson, 39, also would serve as chief counsel of the Internal Revenue Service, succeeding Fred Goldberg.