A local design firm has been added to the group of companies involved in the effort to revamp Baltimore's oldest and once-largest hotel, the Lord Baltimore.

Perlmutter Associates, a Rockville builder and developer which purchased the Lord Baltimore in June, has awarded the interior design work for the $35.5 million renovation to the Bethesda Design Group. Locally, the firm has designed the Bank of Bethesda building and the Metromedia building.

When the construction crews and interior designers finish their work, with a target date set for December 1985, the hotel will reopen as the Lord Baltimore Quality Royale. Quality Inns International, a division of the Silver Spring-based Manor Care Inc., will manage the 21-story, 440-room hotel.

The 56-year-old Lord Baltimore, a city landmark that was once a showcase among East Coast hotels, was closed in 1982 for fire code violations.

Saul Perlmutter, known locally for his development of the Randolph Hills area in Rockville, acquired the hotel for $4.7 million, according to his son and co-owner in the project, David Perlmutter. He has been awarded a $5 million urban development grant by the Department of Housing and Urban Development and a $2 million grant from the city of Baltimore for the renovation.