Pepsico Inc., the nation's second-largest soft drink maker, yesterday reported earnings rose 15 percent in the third quarter to $69.1 million, or 74 cents per share, from $60.2 million, or 66 cents, in the same period last year.

Sales rose 17 percent to $1.1 billion from $938 million in the quarter ended Sept. 9, Pepsico Chairman Donald M. Kendall said.

"The revenue increase in the quarter was paced by substantial gains in the soft drink and snack foods businesses, which represent roughly two-thirds of Pepsico's revenues and three-fourths of its profits," Kendall said.

Besides Pepsi Cola, Pepsico markets Frito-Lay snack products and operates Pizza Hut restaurants.

For the first three quartersif the fiscal year, Pepsico said earnings rose to $166.0 million, or $1.79 a share, from $144.1 million, or $1.57 a share, during the previous year.

Whirlpool Corp. reported yesterday earnings for the third quarter of this year fell by 27 percent on a decline in revenues of 3.2 percent.

Profits for the appliance maker were $22.8 million or 63 cents per share against $31.2 million or 86 cents per share in the three months ended Sept. 30, 1977.

Revenues, including the company's share in profits of affiliates, fell from $560 million to $542 million.

For the first three quarters of the year, profits were down 1.5 percent from $83.7 million or $2.32 per share to $82.5 million or $2.28 per share. Revenues rose 9.2 percent from $1.52 billion to $1.66 billion.

Chairman John Platts said third-quarter sales were flat for the industry as a whole. He said he expected results for the full year to be "fairly comparable" to those for 1977 even though the company might operate below year-earlier levels for the rest of the year.

Salomon Brothers reported general and limited partners' income of $26.5 million before partners' taxes for the fiscal year ended Sept. 30, compared with $55.2 million in 1977.

At Sept. 30 Salomon Brothers' net worth increased to a new high of $208.7 million from $191.7 million at the close of fiscal 1977. It was noted that the 1978 net worth includes $58.1 million in subordinated notes held by banks and insurance companies.

The decline in profitability was attributed to a number of factors, including sharply higher interest rates to finance the firm's substantial inventory of securities, generally higher costs due to inflation and increased expenses resulting from the expansion of the firm's activities, both domestically and internationally.