Citicorp today announced a reorganization of its chief subsidiary, Citibank, and gave sharply increased responsibilities to Thomas C. Theobald, who is considered likely to succeed Walter B. Wriston when he retires as chairman in 1984.

The company said that reorganization of Citibank, the nation's second largest, was undertaken to decentralize its management in anticipation of major growth in its lending and other banking activities in the 1980s.

Theobald, now executive vice president in charge of international banking, will become senior executive vice president in charge of all banking activities with corporation both in the United States and abroad.

John S. Reed, now executive vice president for worldwide consumer banking, also will become a senior executive vice president, although it appears his responsibilities will remain essentially the same.

Theobald, who is 42, "clearly has the inside track to succeed Wriston," said one Citibank insider.

Reed, 40, has guided Citibank's big plunge into consumer banking in recent years, and is considered to be the likely successor to Citibank President William I. Spencer, who at 62 is scheduled to retire in 1982.

But Reed's fate may hang on his ability to turn consumer banking into a profitable venture for Citibank. The bank has spent millions of dollars in recent years to install a host of 24-hour machine banking centers throughout New York City and is also making a big play for consumer loans and bank credit card business.

While Citibank officials admit the consumer business is not yet profitable, they say that they anticipated it would take several years before massive investment in banking machines paid off.

The consumer lending business is also hit hard by current high interest rates, since consumers generally pay less than corporations for loans whenever rates near 12 percent. Corporations today are paying nearly 16 percent for short-term money.

The corporations also announced that Hans H. Angermueller, 55 who is senior vice president and general counsel, will become a senior executive vice president.

The post of senior executive vice president was created by Citibank's board of directors today as part of the restructuring of the company.

Citicorp also announced that former Secretary of Commerce Juanita Kreps, who left the Carter administration last month, will become a member of Citicorp's board of directors.

The reorganization becomes effective Jan. 1.

"It's traditional that a Citicorp chairman pick a successor in his image and Theobald is no exception," said one Citibank official. "Theobald come out of the same international tradition that Wriston did."

Wriston, 60, has been chairman since 1970 and was the chief architect of Citibank's major plunge into international banking in the late 1960s and early 1970s. Citibank has found lending to multinational businesses and foreign governments to be more profitable than its domestic lending although some analysts worry that Citibank and some other major U.S. banks might have too many loans outstanding to foreign countries that are either politically or economically unstable.

Last week, for example, Citibank and several other major banks took control of Iranian deposits to offset loans they had made to the Iranian government or companies it controls. President Carter has blocked all Iranian government deposits in U.S. banks.

The new organization breaks Citibank down into two basic lending divisions: consumer and corporate. Before the structure had been more spread out, withone division handling U.S. businesses in their domestic operations, for example, and a separate division dealing with those businesses in their international operations.

The company said today that the new structure will give greater responsiblity to bank officers within each division to "get decisions made as close as possible to the marketplace."

Within the next five years all of Citibank's top executives will retire. Besides Wriston and Spencer, executive committee chairman Edward L. Palmer is 62 and vice chairman G. A. Costanzo is 63.

Angermueller, although now a senior vice president, is paid more than either Reed or Theobald, who are executive vice presidents.