The Washingtonian magazine has been sold for $3.6 million to Philip Merrill, publisher of Baltimore magazine and the five Capital-Cazette newspapers in Maryland.

Laughlin Phillips, 54, founder and principal stockholder of the 14-year-old monthly, said yesterday that he had made the sale "in order to devote more time to the Phillips Collection," the art museum founded by his father.

Both Merrill and Phillips indicated that they expect the magazine to remain "very much the same," and said editor Jack Limpert has been asked to continue in his position.

"There's a mixture of uncertainty and optimism here," Limpert said yesterday. "I think we tend to take Mr. Merrill at face value when he says he's going to improve management and put more money into the magazine. I certainly intend to stay on."

"I have mixed feelings," said publisher Larry Adler.

"I've only spent a few minutes with Mr. Merrill and we haven't gone into any details."

Announcement of the sale yesterday took the staff by surprise, largely because Phillips has turned down several offers to buy the magazine over the past two years. Limpert was told llate Tuesday, even though negotiations had been in progress for several months, beginning with a luncheon meeting between the two principals at the Cosmos Club just before Christmas.

The first issue of The Washingtonian appeared in October 1965, with a circulation of 15,999. Sales have doubled in the past five years, to a current average of 95,000.The magazine made what Phillips called a "modest profit" in 1975, and then launched an unsucessful book division which drove the company back into the red. In 1977, Phillips said the monthly once again made a small profit.

"We don't have audited figures for 1978 yet," he said, "but it looks like we might have hit six figures."

The actual settlement on the sale is expected in about 10 days, when Merrill personally will take control of the shares of all 47 stockholders in the magazine. The stock then will be transferred to Capital Gazette Newspapers, Inc., of which Merrill owns controlling interests; Landmark Communications of Norfolk, Va., is the only other Capital Gazette shareholder.

Merrill, 44, lives with his wife Eleanor and their three children in Anne Arundel County. He was born in Baltimore in 1934, graduated from Cornell University and Harvard Business School, and from 1957 to 1961 worked for The Newark Evening News, the J. Walter Thompson advertising agency and NBC. He then spent seven years at the State Department during the Kennedy and Johnson administrations as a senior intelligence officer for India and Pakistan. Following a year as a fellow at the University of Chicago, he purchased in 1968 a controlling interest in Capital Gazette Newspapers, publisher of The Annapolis Evening Capital, The Crofton News Crier, The Maryland Gazette and The Brooklyn, Md., News. In 1977, Capital Gazette purchased Baltimore magazine; in the past 18 months, its paid circulation has increased from 5,100 to 40,000.

"I anticipate that we'll combine some of the accounting, bookkeeping and production work of the two magazines," Merrill said yesterday. "There should be some savings from that, but editorially the two magazines will be completely separate."

Phillips said he will enter into a consulting agreement with the new owners of The Washingtonian.

"He was very persistent in trying to buy the magazine," Phillips said of Merrill, "and his ideas for improving it impressed me very favorably. I never thought I would want to do this, but I've got to start raising some funds for the museum and spending more time with my family."