Frederick F. Jackson, the clerk of the Alexandria circuit court and an unopposed Democratic candidate for reelection this fall, died of a heart attack late Wednesday.

Don Henry, chairman of the Alexandria Democratic City Committee, said yesterday that party officials would meet today with chief circuit court judge Wiley R. Wright to determine if the party is permitted under state law to nominate someone to replace Jackson on the ticket.

Jackson, 55, a lifelong Alexandria resident and Democratic party worker, died at about 9:30 p.m. at the family vacation cottage in Colonial Beach, according to Rick Jackson, his son and campaign manager.

Jackson had spent Monday and Tuesday at a circuit court clerks' conference in Charlottesville, and had spent Wednesday fishing near the cottage, his son said. Jackson suffered the heart attack while watching television with his wife Beverly.

Judge Daniel Fairfax O'Flaherty of the Alexandria General District Court yesterday praised Jackson as "a fine, public spirited citizen who ran an efficient office. There never was any backlog of cases here," he said.

Jackson worked for 27 years in the General District Court clerk's office. He was appointed deputy clerk by then-Judge James R. Duncan in 1950, and was appointed clerk of the General District Court in 1960 by the late Judge James Colasanto.

In 1977 when Alvin W. Frinks, then clerk of the Alexandria Circuit Court, unexpectedly resigned with nearly two years remaining in his term of office. Jackson was appointed to replace him.