The modern American woman is ruining the spice business.

At least that's the way the executives of McCormick & Co. saw it today as they explained to their stockholders why the spice maker's earnings were below expectations.

Once the prime purchasers of seasonings from cinnamon to sage, women are leaving their kitchens for offices and consequently eating out with their families in restaurants rather than browsing through super-markets doing what merchants like best -- impulse buying.

During a 25-minute slide presentation today at its annual meeting, McCormick & Co., the world's leader in spices, seasonings and flavors, blamed part of its recent slow growth on the new woman.

Although net income for the company increased by 13 percent last year, McCormick Chairman Harry K. Wells said the increase was "slightly less than expected." Sales last year were $400 million compared with $355 million in 1977.

"Forty percent of American women are working, more meals are eaten away from home," Wells said. By 1981, about 31 percent of all meals will be eaten away from home, he predicted.

Last year, net sales in flavor products and specialty foods sold in groceries increased by 8 percent compared with a 14 percent increase in McCormick's sales of products to the "away-from-home" food service market and industrial processors, according to the company's annual report.

Shoppers also are cutting back on grocery purchases to beat inflation, merchants are keeping smaller inventories and people are making fewer trips to the store, Wells added. Some shoppers are turning to smaller specialty stores to get "the personal touch," he said.

"Despite disappointment in the slow growth in domestic grocery products and food service condiments, we were encouraged by the record performance in both volume and profit growth by many units of the company," Wells said in the company's annual report.

In fact, the company is increasing its hold in supplying the same market that is diminishing its grocery sales: hotels, restaurants, fast-food eateries and other institutions.

The company is producing dehydrated vegetables, basically onions such as those used in fast-food restaurants, and Wells announced today that McCormick is negotiating to acquire the Han Dee Pak Co. of Atlanta, a specialty food-processing firm that makes individual packets of foods such as ketchup and jelly for restaurants.

"It would be a nice addition to our product line," which already had sales of $50 million last year, Wells said. Han Dee Pak had sales last year of $12 million, he said.

Despite the third year of static growth in the grocery store industry, several new products have proved successful, Wells said. They are imitation bacon chips, Lite Gravy (which has 10 calories per serving), and Salad Toppins, a crunchy herb-and-spice addition to salads.

Wells also said the company's frozen chicken patties are in demand.

In fact, McCormick & Co. little resembles the firm which began 90 years ago as a producer of fruit flavors, liniments and tonies. Today, 5,000 seasoning blends are distributed in 84 countries and processed in 39 facilities worldwide; 14 divisions and subsidiaries and one affiliate are located in the United States; seven subsidiaries and five affiliates are outside this country. Maryland Properties Inc., a subsidiary, principally leases industrial and office property.

Principal products are natural spices and herbs, dehydrated vegetable products, specialty frozen foods, sesame seed, food seasoning mixes, cake decorating products, popcorn, condiments and pourable dressings, encapsulated and synthetic flavors, and plastic squeeze tubes.

In other action today Hillsman v. Wilson was named president and chief operating officer of the company, succeeding Wells, who will continue as chairman and chief executive officer.

Wells, who served as president and chairman for two years, said that "multiple duties continue to grow" in size and complexity. "Now is the time to make that move," Wells said.