PARIS — In 2001, when Daniel Wildenstein lapsed into a coma here just days before his death at 84, French authorities say, his two sons and a team of financial advisers began quickly reshuffling the holdings of this wealthy patriarch who had led one of the greatest art dealing-dynasties of the 20th century.

Almost $250 million worth of art was shipped from family vaults in New York to tax havens in Switzerland, the French government’s criminal investigators say in a report; even the ownership of his prized thoroughbred horses was abruptly transferred to a newly formed family company while he lingered unconscious in a hospital bed.

The secret effort was part of a gigantic undertaking, the French authorities say, to avoid an estate tax bill in France and potentially in the United States. The French government has calculated that the estate could owe, with fines and interest, at least 550 million euros, or roughly $600 million, in France alone. Next month, several family members are scheduled to go on trial here on tax fraud and money-laundering charges. The primary targets are Daniel Wildenstein’s son, Guy, 70, who is the president of Wildenstein & Company, based in New York; his entourage of Swiss and French financial advisers; and offshore private banks. (Daniel Wildenstein’s other son, Alec, died in 2008.) Tax fraud carries a maximum prison sentence of seven years, and possibly other fines.

For a family whose limestone mansion gallery was long a landmark of the New York art world and whose legacy includes widely embraced scholarship on Manet and Monet, the trial represents the latest in a series of familial battles, including estate fights, a messy divorce, even allegations of harboring missing art, that have sullied what was once a reputation for discretion and erudition.