The 10-story, 55-year-old former Hamilton Hotel at 14th and K streets NW now is undergoing a multi-million-dollar conversion and upgrading into commercial office and retail space. The work is expected to be completed next summer.

Meanwhile, the 64-year-old Burlington Hotel at 1120 Vermont Ave. NW was closed last week and will be razed early next year as the site of a 500,000-Square-foot office building under a 99-year land lease, according to veteran developer Sylvan Herman. He said architect Peter Ellenbogen is preparing drawings for the 12-storey building.

The Hamilton, recently owned by the Salvation Army which briefly operated the 275-room facility as a home for single girls, has been vacant for a year. It was sold a few months ago to Hamilton Associates Ltd.

The new ownership includes home builders Peter Berman and Robert Berger, plus real estate professionals Melvin Mandell, Robert Holtzman and Robert Moran.

Berman said Monday that the remodeled structure will include an atrium entrance to shopping on 14th Street and a new office entrance on K Street. Cosmopolitan Realty and Robert Moran Associates are handling leasing. The archictect is Edmund W. Dreyfuss & Associates. Ivor B. Clark Co. Inc. arranged mortgage financing with Travelers Insurance Co. and American Security Bank.

A spokesman for the new ownership of the recently closed Ambassador Hotel, on the opposite corner of 14th and K said Monday that a decision still is under study on whether to raze or renovate that 49-year-old, 416-room building into office space or another use.

Adjacent to the Burlington Hotel on the southwest quadrant of Thomas Circle, developer Giuseppe Cecchi and a group plan a large office building, possibly with a condominium apartment on the acre-plus site that now is a parking lot. No construction start is anticipated in 1979.