Major banks reported increased profits yesterday, reflecting continued high demand for loans despite record interest rates.

Citicorp, the holding company for New York's Citibank, the nation's second largest, said that profits for the third quarter rose 16.6 percent to $138.9 million ($1.11 a share) from $119.1 million (96 cents) in the same period last year.

Manufacturers Hanover Corp., the parent of the nation's fourth largest bank, reported profits rose 17 percent to $55.7 million ($1.69 a share) from $47.6 million ($1.46) in the same period last year.

Continental Illinois Corp., owner of No. 7, Continental Illinois of Chicago, reported earnings rose 23.6 percent to $50.8 million ($1.29 share) from $41.1 million ($1.05) in the 1978 period.

Security Pacific Corp., parent of No. 11, Security Pacific National Bank of Los Angeles, reported earnings rose 22 percent to $42 million ($1.52) & share) from $34.4 million ($1.34) a year ago. It noted that stockholder equity in the company passed $1 billion during the quarter.

The figures were before securities gains or losses.

Citicorp said its profits for nine months rose to $390 million ($3.13) from $363 million ($2.93) in the same period last year.

Continental Illinois said its earnings for nine months were $143.8 million ($3.66), up from $121.4 million ($1.04).

Manufactures Hanover said its nine-month income was $159.5 million ($4.86), up from $136.2 million ($4.19).

Nine-month profits at Security Pacific rose to $122.1 million ($4.44), up from $98 million ($3.83).

Two major brokerage companies reported third-quarter profits increases yesterday as the industry benefitted from record stock market volume this summer.

Merrill Lynch & Co., the parent of the nation's largest brokerage firm, said earnings rose 15.6 percent to $37.5 million ($1.03 a share) from $32.4 million (90 cents) in the same period last year.

E. F Hutton Group said earnings climbed 3.6 percent to $11.5 million ($1.77 a share) from $11.1 million ($1.61) in last year's third quarter.

Merrill Lynch said its profits were a record for any third quarter and the second highest for any quarter, surpassed only by the first quarter of 1976.

Revenues at Merrill Lynch rose 22 percent to $528.7 million during the period. Hutton revenues climbed 44 percent to $211.7 million.

For the first nine months, Merrill Lynch reported earnings of $89.1 million ($2.44), up from $62.3 million ($1.74). Revenues rose to $1.46 billion from $1.12 billion.

Hutton said its nine-month earnings were $26.2 million ($3.98), up from $24.5 million ($3.56). Revenues were $530.2 million, up from $382.2 million.

Union Pacific Corp. earned $1.79 a share in the third quarter, up from $1.36 a year ago on a rise in revenues to $976.9 million from $730.3 million. Net income was $85.5 million against $64.9 million last year.

Nine-month profits were $281.7 million ($5.91 a share) on revenues of $2.86 billion compared with $184.5 million ($3.88) a year ago on revenues of $2.16 billion.

Champlin Petroleum contributed $43.3 million to the third-quarter profit, up from $28.5 million a year ago.

Union Pacific Railroad profit was $29.2 million, down from $31.2 million Fuel costs cut the earnings despite a rise in traffic and a gain in revenues to $44.8 million from $369.5 million. The company pointed out that the average price of diesel locomotive fuel has risen from 36 to 67 cents a gallon. a

Georgia-Pacific Corp. earnings for the third quarter were $85 million a 9 percent increase over the $78 million earned in the same quarter of 1978, the company announced yesterday.

Per-share earnings for the quarter were 82 cents compared with 76 cents in the third quarter of 1978. Sales totaled $1.38 billion, a 15 percent increase over sales of $1.2 billion in the comparable 1978 quarter.

The firm's total sales for the first nine months of 1979 were $3.83 billion, up 19 percent over sales of $3.23 billion in the nine-month period last year. Earnings were $257 million ($2.45 a share) compared with $227 million ($2.20) in the first nine months of 1978.

Republic Steel Corp. reported yesterday that its third-quarter earnings were down about 7 percent from the same period a year ago because of a drop in orders during late August and September. The company is the fourth largest steel producer in the United States.

Republic Steel said it earned $28.5 million ($1.76 a share) on sales of $1 billion in the quarter compared with earnings of $30.6 million ($1.89) on sales of $869.1 million in the third quarter of 1978.

For the first nine months of this year, Republic's earnings totaled $110.9 million ($6.85) compared with $71.7 million ($4.43) in the comparable 1978 quarter.

W. J. DeLancey, chairman and chief executive officer, said Republic is not certain how long the slump in business will last.