American Stores Co. announced net earnings for its third fiscal quarter were $30.9 million or 89 cents per share, up 48.33 percent from the $18.84 million or 60 cents per share earned in the same three months last year.

Earnings for the 39 weeks ended Nov. 3 were $96.35 million or $2.79 cents per share, up from $65 million or $1.84 per share for the same period in 1989.Sales for the 13-week third quarter were $5.44 billion, up 3.30 percent over the period a year earlier. Sales year-to-date were $16.44 billion, an increase of 3.69 percent over 1989.

American Stores said third quarter 1990 earnings include gains of 10 cents per share on the sale of assets of the Buttrey Food and Drug Division. The third quarter of 1989 includes earnings of $0.26 per common share from the sale of assets and expenses of 6 cents per share resulting from the San Francisco earthquake.

Average common shares outstanding for the year-to-date were 34.50 million in 1990, up from 30.72 million last year.

The company said there were no preferred dividends in 1990, compared to 1989 preferred dividends of $48,000 for the third quarter and $8.60 million year-to-date.