Outlet Co., the broadcasting and retailing company that owns Washington radio WTOP, announced plans yesterday to sell most of its stores and use the proceeds to buy more radio and television stations.

Bruce Sundlun, president of the Providence, R.I., firm, said an agreement has been signed to sell 91 department and menswear stores to United Department Stores, a privately owned retailer based in Trenton, N.J.

Outlet is to receive $33.5 million in cash and a $5 million note for the stores. Including tax deductions for losses on the sale of the stores, Outlet expects to net about $44.7 million on the sale.

Sudnlun said the funds will be used to reduce debts incurred earlier this year when Outlet purchased a television station serving the Stockton and Sacramento, Calif., market. Outlet, which owns five TV channels and seven radio stations, is considering other broadcasting acquisitions, a spokesman said.

One company can own no more than 7 AM radio stations, 7 FM radio stations and 7 television stations. No more than 5 of the TV properties can be VHF stations.

Outlet Co. gets about 85 percent of its revenues from its retail stores, but earns about 85 percent of its profits from broadcasting, company officials said. In the fiscal year ended Jan. 31, Outlet's revenues totaled $313 million, up from $307 million the previous year, but profits were only $4 million, down from $10 million in 1979.

In an effort to improve earnings, Sundlun has been converting Outlet from a retailing company with a few broadcasting operations into a radio and television firm with minor retail business.

After purchasing WTOP-AM from The Washington Post Co. two years ago, Sundlun pulled out of the Washington retail market by selling Outlet's Phillipsborn and Beyda stores.