Acting Maryland Goc. Blair Lee III, rejecting the recommendations of Prince George's County Democrats, yesterday appointed Republican Francis A. Borelli to the District Court judgeship recently vacated by Richard V. Waldron.

Calling it "the most difficult appointment" he has yet to make as acting governor, Lee said of Borelli, "I don't know the gentleman, but he is highly regarded by most people over there (in Prince George's) as a top-flight attorney."

Lee chose Borelli over two other attorneys - both Democrats - recommended to him by the state Judicial Selection Commission. One of the attorneys, Del. Robert Redding (D-Prince George's) had received the strong recommendation of the Breakfast Club, a group otherwise known as the Prince George's County Democratic Advisory Committee.

Lee said he expected "to get a lot of flak" over the appointment, but added, "I think in that big county, there should be a Republic on the bench."

Traditionally, the recommendation of the Breakfast Club becomes the ultimate decision as to who gets what political plums in the county.

Lance Billingsley, chairman of the county Democratic committee, said the Borelli appointment was "a flat rejection of the opinion of the political leadership of Prince George's County. It is an alienation of the leadership and one that is not very logical."

The Borelli appointment may erode any support Lee was expecting to receive from teh county's Democratic politicians in the 1978 gubernatorial race. "There is little doubt that Steny (State Sen. Steny Hoyer, (D'Prince George's)) is running for governor (against Lee) next year. And (Hoyer) enjoys the support of much of the (county Democratic) leadership," said Billingsley.

Billingsley said he felt Borelli would "do a good job on the bench," but said, "I think that any appointment should be made with the consultation of the local (Democratic) leadership. When it comes to local matters, you should give great credence to the opinion of the people closest to local matters."

Borelli, 47, has been a practicing attorney for 16 years and twice was a candidate for House of Delegates on the Republican ticket.He said he is "very elated" over the appointment and has been on "cloud nine ever since I heard about it.

"Why he appointed me, I don't know, but God bless him," he said.

Borelli, who failed the Maryland State Bar exam the first time he took it after graduating from American University in 1961, said he learned of the appointment when Lee called him yesterday morning and told him "to go get fitted for a black robe."

Sam Ianni, chairman of the Prince George's County Bar Association Judiciary Selection Committee, which recommended Borelli for the judgeship, said he never expected to "see the appointment happen with a Democrat in power. He (Borelli) is well-known as a Republican and I didn't think it would happen." The selection committee also recommended Redding and Bond Haleford.