The executive director of the American Heart Association's D.C. chapter has been fired by the board of directors amid an association investigation of funds that an audit showed have not been properly accounted for, the association announced yesterday.

"The board is deeply concerned and, as you can imagine, this has been a very traumatic situation," Weldon B. MacDonald, chairman of the board of the Nation's Capital Affiliate of the association, said in an interview. "It has been a very grave concern to us all over the past few months."

The executive director, Lonnie R. Merriett, was fired June 1 on a unanimous vote of the 57-member board. Merriett had been scheduled to deliver an annual report at the association's yearly meeting that day. But instead, no report was given and the outgoing president, Dr. Stanley M. Sinkford, announced that Merriett had been "terminated for cause," according to association officials.

In a statement released yesterday, MacDonald said Merriett was terminated "because of questions raised in respect to accounts for which he was responsible." The statement said the sum in question was less than $10,000 and was discovered during an internal audit begun in April.

"Realizing that public contributions are at stake, the board took immediate action to resolve the problem. We have been assured there will be restitutions of the funds," the statement said.

MacDonald referred questions to the association's lawyer, Jacob A. Stein, who said, "The association is seeking to account for its funds and has turned the matter over to its attorney. I have been in contact with Mr. Merriett." Stein declined further comment.

No charges have been filed against anyone in connection with the audit.

Merriett, who lives in Gaithersburg, said yesterday, "My only comment is that the matter is now being resolved." Merriett said, "Discussions are at hand regarding the report of the audit. Where and if necessary, restitution will be made."

Merriett was hired as executive director in October 1981, and has been affiliated with the American Heart Association for 11 years. He worked at chapters in Michigan and St. Louis before taking an administrative job with the Los Angeles chapter in 1979, a job he held until coming to Washington.

An interim executive director, John Gould, has been dispatched from the national headquarters of the American Heart Association in Dallas to temporarily take over Merriett's duties, which include supervising the chapter's 12-member staff and coordinating the association's daily operations.

Dr. Alan M. Weintraub, a Chevy Chase cardiologist who is the newly named president of the chapter, said yesterday that a search for Merriett's replacement will begin this week. He termed it "a sad situation" but declined further comment.

Founded in 1928, the Washington Heart Association was aimed at reducing the premature deaths and disabilities caused by cardiovascular disease, the leading cause of death in the U.S. The local group joined the American Heart Association in 1948 and is one of the more active of the 55 chapters in the nation.

In the fiscal year that ended last June, the D.C. chapter raised $903,035 from public donations, legacies and bequests, and other sources. The association spent $772,840 last year. Of that amount, $439,625 went to fund research, health education, and community services, while $146,164 went toward management, general expenses and fund raising.