RCA Corp., whose top management chair doesn't seem to stay warm for long, will soon get its fourth chairman in less than two years.

Edgar Griffiths, chairman and chief executive officer of the huge conglomerate -- which owns the NBC radio and television, a global communications network, Hertz Rent-a-Car and CIT Financial Corp., and is the largest U.S. manufacturer of television sets -- has resigned effective July 1, according to the RCA board of directors.

Thornton Bradshaw, 63, president of Atlantic Richfield Co., the nation's seventh largest oil company, will succeed him.

RCA's record $8 billion in sales and $315 million in profits last year were achieved largely because of the acquisition of CIT. The NBC television network is mired in third place in the ratings race with CBS and ABC, and had it not been for the acquisition, income would have fallen.

The past year at RCA has been marked by controversy, with the forced resignation of RCA president Maurice Valente, a former top executive at International Telephone & Telegraph and Griffith's hand-picked successor and of NBC chairman Jane Cahill Pfeiffer.

But RCA vice president Leslie Slote said that Griffiths "asked to be relieved of his duties, effective July 1, because he has been with the company for 33 years and he felt that it was time to get out." He denied reports that once again the board had acted to force a chairman to resign.

Bradshaw said in a telephone interview, "The whole thing is very straightforward. Ed Griffiths has been talking about early retirement for some time."

Griffiths will remain a director and become chairman of the board's finance committee and will serve as a consultant for five years after his retirement at the age of 65, Slote said.

RCA is not the only parent corporation of a TV network to have management upheavals. For instance, CBS president John D. Blacke was unexpectedly fired last May, the second heir-apparent to chairman William S. Paley to meet that fate.

Griffith's departure from RCA's top job is less abrupt than that of his two predecessors, Robert W. Sarnoff and Anthony Conrad. Sarnoff, son of RCA's founder, David Sarnoff, was forced out by the board in late 1975 amidst allegations of "absentee managment" associated with extensive foreign travel that Sarnoff critics said coincided with concert tours of his wife, Metropolitan Opera soprano Anna Moffo.

Conrad was named president and then chairman in June 1976. Before the year was out, however, he too, was forced to quit when it was disclosed he had failed to file personal income tax returns for five years. The reasons for his failure to file, even though most of his income had been subject to withholding and little additional tax was due, has never been fully explained.

Bradshaw, who will get a five-year contract, despite RCA's usual age 65 retirement policy, is familiar with the company's operations because he has been an outside director since 1972.

He said it was premature to talk about plans for improving the conglomerate's performance, but added, "RCA is a strong postion. It's got spots marked out that just position it well to take advantage of the expansion in communications, however it develops. The trick is to foresee those developments. RCA has all the pieces and they've got the talent."

"The communications business -- I like it," said Bradshaw, who has frequently served as a sophisticated spokesman for the oil industry and who has been chairman of the London Observer, which was bought by Atlantic Richfield a few years ago to save it from Bankruptcy.

Bradshaw's switch came as a surprise to other Atlantic Richfield executives, though they knew he had been considering other offers, including the presidency of the University of Southern California last year. Bradshaw's plan to leave Atlantic Richfield sometime in 1982 -- but not to retire -- had long been known.

By coincidence, the Atlantic Richfield board is to meet today to publish the company's 1980 earnings and will name a successor to Bradshaw. Almost certainly it will be William F. Kieschnick, 57, vice chairman of the board and the corporation's No. 3 executive.

Kieschnick for the last two years has effectively been Atlantic Richfield's day-to-day operating chief while chairman Robert O. Anderson remained chief executive officer. Bradshaw increasingly had been the corporation's "outside man," making speeches and public appearances and overseeing some operations such as the Observer, a company executive said.