Marriott Corp.'s plans to buy the Denny's Inc. chain of 1,200 coffee shops, disclosed last week, reflects the international hotel and food service conglomerate's strategy of acquiring businesses that it cannot grow easily on its own while at the same time targeting market niches.

"The company's interest is not to grow by acquisition simply to grow," said John J. Rohs, who tracks the company for the Wall Street firm of Wertheim & Co.

"Their acquisitions are undertaken only when there are significant strategic benefits that can be gleaned from an acquisition and only when it would be very long or costly through internal development," Rohs said.

Marriott and Denny's are still negotiating the deal. But if it is completed, Marriott will go from being the second-largest operator of family restaurants, with its Big Boy chain of 900 restaurants, to being No. 1.

Some Big Boy restaurants will likely be converted to Denny's in the Northeast. Elsewhere, some of the Big Boy restaurants, mostly franchises that don't yield much revenue, will be sold, analysts said. However, the company will not say what its plans are.

"I think the bulk of Big Boy will be disposed," said Joseph Doyle, an analyst with Smith Barney. "The strategy is they want to be in with the dominant players."

J.W. Marriott Sr. began his Bethesda-based company 60 years ago with a nine-stool root beer stand that evolved into 15 Washington-area Hot Shoppes restaurants. Since then, Marriott has become a $5.2 billion business and the nation's ninth-largest corporate employer, with nearly 200,000 workers.

The company has diversified its hospitality services from Sun Line Cruise Ships in 1971 to two Florida and South Carolina time-share vacation resorts. It also is developing retirement communities as a way to ensure growth, analysts say.

Hotels, nonetheless, have been key to Marriott's growth, with the company concentrating on starting its own chains and developing new products.

In 1983, the company launched moderately priced Courtyard by Marriott hotels. It will invest $2 billion by the early 1990s in upscale all-suite hotels that emphasize large rooms, and "compact" hotels that cater to businessmen who hold small meetings.

In 1988, eight Fairfield Inns will open for travelers on a budget. Rooms will go for less than $40 a night -- a far cry from the presidential suite at the New York Marriott Marquis, which comes with a grand piano and costs $2,500 a night.

"There is a lot of segmentation that's going on in the hotel business," said Robert T. Souers, a company spokesman. "Travelers are sophisticated and have many wants and needs. In addition to that we saw there would be a finite . . . ability to grow the traditional business" of standard 350-room Marriott hotels, he said.

The company seldom passes up a chance to buy into the right new niche at the right price. Marriott is buying Residence Inn Corp., a chain with 93 hotels open and 40 under construction or development that caters to one of the fastest-growing segments of the hotel business -- the traveler on an extended stay.

"They want to be in every nook and cranny with the best player," said analyst Doyle.

What Marriott couldn't do in its contract food services division through development it also did through acquisition.

In 1982, Marriott bought Host International, a leading operator of airport terminal restaurants and shops. In 1985, Marriott snapped up Service Systems and Gladieux, food service companies for businesses, health care and educational institutions. Last year, it spent $500 million to buy Saga Corp., a food service management company that added 1,000 accounts to Marriott.

"Marriott had less of a primary interest in airport food services and institutional food services," said James M. Meyer, an analyst who follows the company for Janney, Montgomery, Scott.

"Marriott upgraded themselves from less than No. 1 to No. 1 in airport concessions with Host, and to being No. 1 in institutional food services with Saga," Meyer said.