After a couple of months in the deep freeze, Uncle Sam is starting to fill some of the nearly 1,000 vacancies in the $50,000-per-year Senior Executive Service.

Exemptions have been granted to Defense, Labor and Office of Management and Budget, and they are looking for about 20 specialized experts to fill career jobs in various fields. Most of the SES positions and vacancies are in metro Washington.

Air Force wants somebody to run its meteorology division in Bedford, Mass.; a chief scientist at Eglin AFB, Fla., and a technical director in San Antonio . . . Army needs a director of research at the Huntsville (Ala.) Missile Command . . . Defense wants a director of defense plans to work with NATO in Brussels.

Closer to home, Defense, in Arlington, wants a director for counterintelligence . . . Labor is looking for six associate solicitors here . . . Navy needs a chief scientist for telecommunications, an associate director for finance, somebody to head its labor-management program and a personnel chief for the Navel Material Command.

Office of Management and Budget, which has been running President Reagan's freeze, is looking for someone in government to be the chief of its Interior Department branch. Great spot for an Interior-type who knows where the bodies are buried. Officials expect that more SES jobs -- there are hundreds of vacancies -- will be defrosted in weeks ahead. OPM puts out a weekly bulletin of SES openings. But job-hunters must apply dicrectly to the agency with the vacancies.