Citicorp, the nation's largest bank holding company, said yesterday its profits fell 9.5 percent in the third quarter as its allowance for possible loan losses grew and its operating expenses rose.

Continental Illinois Corp., the parent of Continental Illinois National Bank & Trust Co., which is trying to rebound from big losses linked to problem loans, reported sharply lower profits in the third quarter and large losses for the first nine months.

And in other earnings reports yesterday, Weirton Steel Corp. said it had a third-quarter profit of $15.8 million, its third consecutive profitable quarter since employes bought the mill in January. PepsiCo Inc. said improved performances in its soft drink, food products and restaurant divisions helped boost profit 24 percent. NCR Corp. said net income, revenue and orders all reached record levels, and B. F. Goodrich reported third-quarter profits jumped 81 percent from a year earlier. Citicorp, based in New York and the parent of Citibank, said profits in the third quarter fell to $200 million ($1.42 a share) from $221 million ($1.66) from a year earlier.

Citibank is the second largest bank in the United States after Bank of America in San Francisco, which is a unit of the second largest holding company, BankAmerica Corp.

Citicorp said its results reflected a strong performance in corporate banking in the United States, in important elements of its U.S. consumer banking businesses and in its operations on behalf of other banks in world markets.

But it added that those gains were offset by a significant slowdown in Latin American corporate business, reduced earnings from bond and foreign exchange trading, higher interest rates and anticipated losses from the acquisitions of Citicorp Savings of Illinois and Florida.

The allowance for possible loan losses was increased to $861 million, or 0.89 percent of all loans, as of Sept. 30 from $728 million, or 0.84 percent of all loans, a year earlier.

For the first nine months of the year, profits fell 4.6 percent to $629 million ($4.55) from $659 million ($4.99) in 1983. Continental Illinois said profits in the third quarter plunged 80 percent to $4 million (0.6 cent a share) from $20 million (50 cents), a year earlier. And for the first nine months of the year, the holding company reported a $1.1 billion loss, against earnings of $83 million ($2.06) in the same period of 1983.

Last month, Continental's shareholders approved a $4.5 billion rescue package that gave the Federal Deposit Insurance Corp. 80 percent ownership of the company. Top management of the bank had been replaced earlier as a condition for the largest bank rescue in U.S. history, which included the transfer of about $3 billion in problem loans to the FDIC. Weirton Steel Corp. said its earnings came on sales of $256.1 million. The Weirton, W. Va., company does not disclose figures for the unit's performance in the same period a year ago when it was owned by National Intergroup Inc.

Weirton's sales revenue fell 17 percent from the previous quarter, however, and its shipments fell 21 percent to 485,171 tons of steel, the company said.

It attributed the decline from the previous quarter to poor market conditions.

For the first nine months of the year, the steel maker has earned $48.3 million on sales of $845.5 million, spokesman Chuck Cronin said.

Weirton Steel's 8,200 workers bought the plant from National Intergroup in January, creating the nation's largest employe-owned company. PepsiCo Inc. reported profits of $118.3 million ($1.14 a share) in the three months ended Sept. 8. That compared with profits of $95.2 million (93 cents) in the same period last year.

Revenue rose to $1.93 billion in the third quarter from $1.8 billion a year earlier, PepsiCo said.

For the first nine months, PepsiCo's profit fell to $122.9 million ($1.34), from $206.9 million ($2.10) a year ago. Revenue rose to $5.42 billion from $4.9 billion.

The company said the profit decline for the first nine months was due to second-quarter after-tax charges of $136 million stemming from restructuring actions. It said if the charges were not included in the nine-month results, profits would have risen 25 percent from a year earlier to $259.2 million, including income from discontinued operations. NCR Corp. net income, a record for the quarter, rose to $96.9 million, an increase of 38 percent more than the $70.2 million reported for the year-earlier period, the company said.

Earnings per share, also a third-quarter record, were 95 cents compared with 64 cents for the comparable period last year, a 48 percent gain.

Revenue for the quarter advanced to a record $956 million, an increase of 9 percent more than the $877 million reported for the year-earlier period. B. F. Goodrich Co., based in Akron, Ohio, said its profit was in large part because of a one-time gain from tax-law changes. Without the gain, net income was up 23 percent on a 3 percent gain in sales.

In the third quarter, earnings climbed to $25.5 million (1.07 a share) from $14.1 million (60 cents) a year earlier. The tax gain totaled $8.1 million.

Sales edged up to $878.1 million from $852.7 million.

For the first nine months of 1984, Goodrich said earnings rose to $67.8 million ($2.82) from $12.4 million (44 cents) in the comparable 1983 period. Nine-month sales rose to $2.6 billion from $2.4 billion.