Lower effective tax rates as well as sales gains contributed to increased earnings last year by PepsiCo. Inc., the soft drink and snack food combine.

PepsiCo said yesterday it earned $2.85 a share last year, up from $2.43 in 1978, as sales rose to $5.09 billion from $4.3 billion.

Net income climbed to $264.85 million from $225.77 million.

Final quarter profit was $66.52 million (73 cents a share) on sales of $1.61 billion, compared with $59.8 million (64 cents) a year ago on sales of $1.4 billion.

Chairman Donald M. Kendall said the company also had higher interest costs. Earnings were up 11 percent before the impact of taxes and interest charges, Kendall said.

The soft drink and snack food businesses outpaced PepsiCo's food service, transportation and sporting goods operations, he said.

Litton Industries Inc., reported earnings of $2.11 a share in its second quarter ended Jan. 1, up from $1.23 a year ago on a rise in sales to $1.048 billion from $1.038 billion.

The earnings included $1.77 a share from operations and a capital gain of 37 cents a share, but they were reduced 3 cents a share by losses on currency translations.

Net income was $82.4 million against $50.29 hillion a year ago.

For the half, Litton earned $3.52 a share, including the 37-cent capital gain, up from $1.48 a year when operating earnings were slashed 17 cents a share by currency translation losses.

Net income was $137.97 million on sales of $2.001 billion, compared with $59.65 million a year earlier on sales of $1.980 billion.

Operating earnings for the half were up 82 percent.

Warner-Lambert Co., the pharmaceutical house, reported fourth quarter earnings of $709,000 (one cent), compared with $39.91 million (50 cents) a year earlier.

Fourth quarter sales were $838.51 million compared with $809.77 million in the same period a year ago.

For the year, the company earned $12.4 million ($1.55) on sales of $3.22 billion, down from $207.95 million ($2.61 in 1978 on sales of $2.88 billion.

The profit shrinkage was caused mainly by write-downs on the phase out of the Parke-Davis plant in Detroit and the write off of certain dental products and a lens plant.

Kellogg Co., a leading convenience food processor, said profits increased 12 percent last year to $162.6 million ($2.13 from $145.1 million ($1.90) in 1978.

Sales rose 9 percent to $1.85 billion from $1.69 billion, the cereal maker said.

For the fourth quarter, Kellogg earned $28.7 million (38 cents) on sales of $466 million. In the comparable 1978 period, Kellogg reported profits of $25.1 million (33 cents) on sales of $426.2 million.

Revlon Inc., the cosmetics giant, reported fourth quarter 1979 earnings of $1.34 a share, compared with $1.19 a share for the same quarter a year ago.

Net income was $44.75 million on sales of $499.15 million, compared with $38.83 million a year earlier on sales of $44.47 million.

For the year, net income climbed to $152.69 million ($4.60) on sales of $1.718 billion, compared with $129.23 million ($4.04) on sales of $1.451 billion.

There were 1.2 billion more shares outstanding in 1979 than in 1978.

R.H. Macy Co., the department store chain, reported it earned $5.24 a share in its second quarter ended Feb. 2, up from $3.87 a year earlier, on a rise in sales to $797.29 million from $666.6 million.

Macy's stock is to be split three-for-two March 5. On that basis, the earnings are equal to $3.09 a share proforma against $2.58 a year earlier.

Net income was $55.15 million against $40.5 million a year ago.

First half profit was $77.84 million ($7.40 on sales of $1.36 billion against $5.7 million ($5.11) a year ago on sales of $1.15 billion. The sales gain was 15.9 percent.

After adjustment for the upcoming stock split, the first half profit is equal to $4.93 a share against $3.41 a year ago pro forma.