American Stores Co. said its $4.55 billion in sales for the 13-week second quarter ended July 30 increased 28.5 percent over sales of $3.54 billion for the second quarter of 1987.

Net earnings, which include operating results of recently acquired Lucky Stores, for the quarter fell, however, from $36.46 million, or 98 cents per common share at the end of last year's second period, to $30.27 million, or 79 cents per common share, at the end of the same period this year.Sales year-to-date increased 16.6 percent to $8.15 billion compared to sales of $6.99 billion in 1987. Net earnings for the 26 weeks ended July 30 amounted to $57.32 million, or $1.48 per common share, compared to $71,47 million, or $1.90 per common share, for the comparable period of the prior year.

The above second quarter sales and net earnings for American Stores Co. include the results of operations for Lucky Stores Inc. from June 2 through July 30 as well as the additional interest expense and amortization of asset write-ups relating to the Lucky Stores Inc. acquisition, a spokesman said.

For comparison purposes, American Stores Co. earnings per common share, excluding the effects of the Lucky Stores Inc. acquisition, increased 37.8 percent to $1.35 per common share from 98 cents for the second quarter of 1987.

The year-to-date earnings per common share, excluding Lucky, were $2.04 vs. $1.90 for the prior year. American's like store sales increased 5.7 percent for the second quarter and 5.4 percent year-to-date.

American Stores Co., excluding Lucky, had an operating profit of $104.33 million or an increase of 8.2 percent compared to the prior year second quarter. Year-to-date operating profit for American Stores Co., excluding Lucky, decreased 5.5 percent to $179.08 million.

The year-to-date and second quarter sales and earnings were impacted by the company's strategy of increasing sales in existing stores at Acme Markets Inc., Skaggs Alpha Beta/Buttrey Food Stores and Alpha Beta Co., the spokesman said.

American Superstores Inc. the company's eastern grocery operations, had a 5.6 percent sales increase for the second quarter to $1.74 billion compared to $1.65 billion in 1987.

Like store sales increased 4.5 percent for the second quarter of 1988 compared to an increase of 1.8 percent in like store sales in the second quarter of 1987.

Year-to-date sales increased 5.8 percent to $3.44 billion from $3,25 billion in 1987. The year-to-date like stores sales increase is 4.9 percent compared to 1.3 percent for the prior year results.

Lucky Stores Inc. is included in the American Stores results for the period from June 2 to July 30. Only Lucky's continuing operations in California and Nevada are included.

Lucky's Arizona stores were sold on Aug. 12 and Lucky has entered into contracts to sell their Florida division, Kash 'n Karry, at the end of September 1988 as well as the 37 Alpha Beta and Lucky stores listed for disposition by the Federal Trade Commission. Lucky sales included American Stores' second quarter operations were $823,697,000.

The year-to-date like store sales increase for Lucky's continuing operations was approximately 7.3 percent. Operating profit from June 2, to July 30, which is included in the American Stores consolidated results amounted to $39.51 million.

The additional pre-tax interest expense and the amortization on the asset write-up of Lucky Store's Inc. for the same period was approximately $48 million.

The average common shares outstanding for the year-to-date were 30,169,000 compared to 31,014,000 in 1987.