Prince George's County Council member Sarah Ada Koonce, who in 1962 became the first woman to win a state delegate seat in that county, will replace Fred L. Wineland as Maryland's secretary of state, according to sources within the county.

The sources said Koonce, 59, will serve at least until January, with the expectation that she will be considered a favorite to retain the job. Wineland announced three weeks ago that he will resign this month to devote more time to his family and his business.

Lou Panos, press secretary to Gov. Harry Hughes, would not confirm the report, saying only that a number of people are being considered. "I did understand that they were thinking about making some sort of temporary arrangement," he added.

The sources said Hughes, who has made clear he is committed to appointing a woman to the part-time post, made the decision yesterday and informed a handful of local leaders through an intermediary.

The selection of Koonce would resolve a number of political problems for the dominant Prince George's Democratic organization, which because of redistricting, faces the possibility of seeing the quiet, agreeable Koonce end her 20-year career in politics. As a result of last fall's councilmanic redistricting process, Koonce, a two-term council member, was placed in the same district with her friend and fellow incumbent David Hartlove. At-large council member Sue V. Mills, an aggressive campaigner who was the second highest vote-getter in 1978, subsequently announced that she also intends to move into the district.

Faced with a three-way race, Koonce filed Thursday as a candidate for clerk of the Circuit Court. In that race, however, she would face incumbent Norman L. Pritchett, who along with Wineland is a longtime friend and ally from the closely knit southern end of the county.

State Sen. Thomas V. (Mike) Miller, asked to comment on the choice of Koonce, said, "I guess the governor just felt he wanted to help Prince George's County. We lost a lieutenant governor, we lost a secretary of State . . . and we also had a problem down here. This solves it."