The Marriott Corp. broke ground this week on a senior citizen complex in Florida, reflecting what a company executive said is a billion-dollar new direction for the hotel company.

Retirement housing "will be a significant part of the Marriott Corp. in the next 10 years," said Brian Swinton, a vice president of Marriott Senior Living Services, a division of Marriott Corp, based in Bethesda, Md."We'll be spending over a billion dollars" on developing about 150 retirement complexes over the next five to seven years, Swinton said in a telephone interview after the groundbreaking of the new project in Boca Raton.

Noting the growing proportion of people over age 65 in the United States, Marriott began research into the senior-citizen housing business in the early 1980s.

In the late part of the decade it began managing nine existing residential communities and opened two specialized communities, one serving a university area outside Philadelphia and one designed primarily for military retirees in Virginia.

The company has developed two prototype "assisted- living" communities that it will build in Florida and then adapt for metropolitan areas nationwide, Swinton said.

Marriott's research has found that older people have five concerns about housing - the "financial integrity" of the retirement community, personal security, services, quality food and a non-institutional environment, Swinton said.