Marriott Corp. DESCRIPTION: An international food and lodging company with more than 100 hotels and 40,000 rooms, 1,600 company operated and franchised restaurants in the Roy Rogers, Big Boy and Hot Shoppes chains plus airport and in-flight catering, amusement parks and cruise ships (NYSE). FOUNDED: 1926. TOP EXECUTIVES: J. Willard Marriott, chairman; J.W. Marriott Jr., president and chief operating officer

Marriott's toughest job this year will be avoiding indigestion from simultaneously swallowing Gino's fast food operations and Host International's airport food business. The $48 million acquisition of Gino's and the $148 million purchase of Host are the biggest outside expansion efforts for a company that has had no trouble generating internal growth. The economic slowdown is hurting hamburger and other fast food sales, but not stalling Marriott's growth.

Maintaining an almost 25-percent-a-year growth in hotels, Marriott added 23 hotels last year and has 18 more planned for 1982. More than 200 Gino's will be converted to Roy Rogers to keep the restaurant division growing, and Host will keep up the expansion of the contract food service division. This year's financial innovation for Marriott is a soon-to-be offered limited partnership that will provide tax shelters for investors and hotel financing for Marriott.

Manor Care Inc. DESCRIPTION: A nursing center and hotel company in Silver Spring that operates nursing homes, alcohol rehabilitation centers, a hospital and owns the Quality Inn lodging chain (AMEX). FOUNDED: 1968. TOP EXECUTIVE: Stewart Bainum, chairman and chief executive officer.

Since Bainum consolidated his controlling interests in Manor Care and Quality Inns into a single company in December 1980, the health-care division has continued to grow at a steady pace, but the lodging chain is taking off. Hiring away the management team that ballooned the Best Western motels from 800 units to 2,500, Quality Inns added 75 new franchised properties with 10,000 rooms last year and is seeking 15,000 more rooms this year.

Repositioning the chain has created separate Quality Royale, Quality Inn and Comfort Inn groups linked by a new computerized reservation system in Silver Spring. Manor Care, meanwhile, will add a new alcoholic rehab center in New Orleans, another in Philadelphia and a Charleston nursing home this year and has five more projects on the drawing board.