The parent company of the financially troubled 50-unit Korvettes department store chain said today it had agreed to sell the entire operation to a French concern, instead of a majority interest.

The initial agreement, announced last October, called for the sale of 51 percent of the Korvettes unit to the Agache-Wilot Group, a French manufacturing and retailing company.

But Arlen Realty & Development Corp., the parent company of Korvettes, said the agreement had been modified to transfer ownership of the entire subsidiary. Arlen said the sale was expected to take effect March 15.

Terms of the modified agreement called for a $55 million investment, including $15 million infusion of new capital into Korvettes. The $40 million balance includes assumption of certain debts of Arlen and installment payments to the real estate company.

Korvettes stores lost $1.9 million on sales of $250 million in the first six months of last year and posted a net loss of $6 million in 1977.

Under the initial agreement announced last fall, Agache-Willot agreed to provide new equity capital for Korvettes with an initial commitment in excess of $30 million and options to expand its investment at a later tiem.

The Agache-Willot Group is a major European retailer and manufacturing with estimated sales of $2 billion last year.