RCA Corp., filling a slot that had been vacant for more than two years, today announced that Robert R. Frederick, a veteran of 34 years with General Electric Co., will take over next week as RCA's president and chief operating officer.

Frederick, 56, is likely to succeed Thornton Bradshaw, 65, as chairman of the troubled conglomerate when Bradshaw relinquishes his post. In an interview, Bradshaw praised his hand-picked heir apparent and said that Frederick would not get the top RCA job only if he "fell on his face."

"This is is my major contribution to RCA," Bradshaw said. "I will have failed in everything if" Frederick does not match expectations, he added. Bradshaw became RCA's chairman in July 1981 and has spent much of the last six months reviewing candidates for the number two post.

RCA, which has suffered through years of turbulence at top levels of management, has had no president since Maurice R. Valente was forced to resign the job in June 1980. In contrast, Frederick has never worked anywhere beside GE.

Frederick currently runs GE's International Sector. From 1977 until 1979, he was a GE senior vice president and was in charge of corporate planning.

Frederick also was general manager of GE's color television division and was group executive for consumer products group, a branch of GE that included broadcasting and cable television ventures -- areas that closely match major RCA's interests.

Bradshaw said Frederick's appointment, already approved by an RCA executive committee, but due to come before the board next month, will permit him to spend less time at monthly business review meetings. "He will take that over," he said.

Bradshaw will retain direct supervision, however, of the National Broadcasting Co., as well as key corporate staff functions -- legal and financial affairs, and industrial and public relations.