ATLANTA (AP) _ Five months after spurning a takeover bid from NCNB Corp., Citizens and Southern Corp. has agreed to a $4.7 billion merger with Virginia-based Sovran Financial Corp. to create the nation's 14th-largest banking company.

Atlanta-based C&S and Sovran announced the deal Tuesday, saying the merger has been discussed over the past two years. The combined banks, which will maintain separate headquarters under a new holding company, will have assets of $47 billion and 976 offices in seven states plus Washington, D.C.

The new company will be calle Avantor Financial Corp.

''We are creating a large, nationally competitive franchise with a powerful presence in major high-growth markets, and we're underwriting it with superior credit quality,'' the two banks said in a joint announcement.

''We feel it's a perfect fit,'' said C&S spokesman Scott Scredon. ''We don't overlap, our management cultures are very similar, and we each double our market presence. We both feel it couldn't be any better.''

In terms of assets, the merger would create the nation's 14th-largest bank holding company.

The friendly nature of the merger was in stark contrast to the mood in April, when Charlotte, N.C.-based NCNB targeted C&S in a $2.4 billion takeover bid that would have created the nation's sixth-largest bank.

Bennett A. Brown, C&S chairman and designated head of the combined company, told securities analysts in New York today that the C&S-Sovran merger wasn't in reaction to NCNB's unwanted offer. ''We started conversations two years ago,'' he said.

NCNB also issued a statement today dismissing speculation that it might want to re-enter the picture, since its previous offer would now be worth about $54 a share, substantially higher than the approximately $34 of stock that C&S shareholders would receive under the merger with Sovran.

During a tense, monthlong courtship by NCNB, C&S officials refused even to discuss the deal. NCNB eventually withdrew the offer, saying it did not want to get involved in a long fight.

Brown said C&S' board of directors saw greater long-term value in the deal with Sovran than in the ''short profit'' shareholders would have received from NCNB.

''This is an extremely friendly deal,'' said Lacy Shockley, a banking industry analyst with Smith Barney, Harris Uphan & Co. in New York. ''NCNB was unusually hostile. Here, you have two very similar banks. This is the truest merger of equals I've ever seen.''

Ginny Mackin, an NCNB spokeswoman, Tuesday declined to comment on the C&S- Sovran merger. ''We don't comment on what other banks do,'' she said.

Scredon said the boards of the two institutions approved a definitive agreement Tuesday. He said final approval from shareholders and regulatory agencies is expected during the first quarter of 1990.

Under the merger agreement, each of Sovran's 59.8 million shares of outstanding common stock will convert into 1.23 shares of the new company's common stock.

Each of C&S' 62 million shares of outstanding common stock will convert into one share of the new company's common stock, worth about $34.87.

C&S Chairman Bennett A. Brown will become chairman and chief executive officer of the new company while retaining his position at C&S. Sovran Chairman Albert B Gornto will become chairman of the new company's executive committee and will retain his position at the Norfolk, Va.-based bank.

Dennis C. Bottorff, president and chief operating officer of Sovran, will be president and chief operating officer of Avantor and become chief executive officer of the new company upon Brown's retirement. At that time, Hugh Chapman, now president of C&S, would become chairman of Avantor.

C&S has 489 bank offices in Georgia, Florida and South Carolina. Sovran has 487 offices in Virginia, Maryland, Tennessee, Kentucky and Washington, D.C.

''It's a big deal,'' said Ms. Shockley. ''It's going to create the powerhouse in the Southeast.''

She said the merger is likely to spur more such activity in the region. ''It puts pressure on other Southeastern banks to do something,'' she said.

Katherine Hart, an analyst at Interstate Johnson Lane in Atlanta, said, however, that while the merger greatly increases the banks' presence, it is premature to predict what effect it will have on earnings.

''Size itself does not make you automatically better than everyone else,'' Ms. Hart said.