Jane Cahill Pfeiffer, the former IBM executive who turned down President Carter's offer to become the first woman commerce secretary, will be the new chairman of the National Broadcasting Company, it was announced yesterday.

Pfeiffer, 45, was suggested for the post by NBC president and programming whiz Fred Silverman who said he will submit her name to the network's board on Oct. 4, the same day she will stand for election as a director to the board of RCA, the parent of the wholly owned subsidiary.

The NBC chairmanship is the highest post ever attained by a woman at any of the three networks. But although Pfeiffer will be chairman, she will not be network chief.

"I will be working for and reporting to Fred," she said in a transatlantic telephone interview. "It may be a bit unusual outside of the broadcasting arena, but typical of broadcasting organizations."

Pfeiffer first got to know Silverman when he was head of programming for CBS television and she was responsible for IBM's entry into television advertising an area that expanded significantly under her supervision.

Interestingly, she was also the intermediary who approached Silverman early this year on behalf of RCA Chairman Edgar Griffiths to see if Silverman could be lured from No. 1 ABC - which he was instrumental in making the ratings leader - to third place NBC. (See TV Column D18.)

Pfeiffer has been acting as a consultant to RCA since last November. She has been doing consulting work for a number of companies since she left IBM in 1976 where after 20 years with the company she was vice president for communications and government relations. TPfeiffer was also President Carter's first choice to be his secretary of commerce, but she turned him down for family and personal medical reasons. He then turned to Duke University economics Professor Juanita Kreps, who became the first female commerce secretary.

Coincidentally, announcement of her appointment comes just as NBC is previewing a new series, "W.E.B." about the travails of a female executive battling for power in the male-dominated corporate suites of a fictional television network.

The series character, however, does not become network chairman.

As NBC chairman, Pfeiffer will concentrate-on governmental relations, legal affairs, long range planning and employee relations, the network said in its announcement. That would allow Silver to concentrate on programming, his forte.

"Beyond that," according to Silverman, "Jane will be working along with me on all aspects of NBC's operations, and will have an active role in policy and administrative decisions."

Silverman, in his statement, said he was "Delighted to have her at my side." Since Silverman's arrival at NBC in June, Pfeiffer, at his request, has been working closely with him.

Pfeiffer, reached by telephone in France, where she is on a business trip with her husband, Ralph Pfeiffer Jr., an IBM senior vice president, also said she was "delighted to have this opportunity to work with Fred and help make television what all of us would like it to be."

She said that besides her main duties in representing NBC in Washington and other public forums," Fred and I will be working together on the programming side - including radio, news and sports."

I would like to see us do more work in the area of quality programming," Pfeiffer said. "The whole way we bring information to the American people can be improved. There's a lot of good the median can do, and I'like to work in that field."

She said her main broadcasting experience up to now "comes from being a sponsor on television shows."

Pfeiffer meanwhile disclosed that in December 1975 she had an operation for thyroid cancer, but added that "that problem won't come back again."

She will be replacing Julian Goodman as NBC chairman. Goodman, who used to head NBC News, has held the chairmans post since 1974, and Silverman said he will propose that he become chairman of the NBC Executive Committee.

Pfeiffer was bron in the District of Columbia in 1932 and put herself through the University of Maryland. She joined IBM as a trainee in 1955, and in 1960 she was named site manager for the computer firm's Bermuda missile tracking station during the Mercury space program.

She took a leave of absence from IBM in 1966 to become the first woman White House Fellow.