It has become a familiar story of late. The heirs of a Jewish art collector discover that paintings seized by the Nazis during World War II were never returned to the family. They start searching and, occasionally, they are lucky. A work is traced to a museum or spotted at an auction and, after lengthy negotiations, the rightful owners recover it or receive compensation.

But what happens when virtually an entire collection is lost?

This is the challenge facing the heirs of Jacques Goudstikker, Amsterdam's leading prewar collector and dealer in Dutch and Italian old masters. Last month, after eight years of dillydallying, the Dutch government finally agreed to return 202 of his paintings, which had been hanging in Dutch museums since the 1950's. Another 1,000 or so are still missing.

Enter Clemens Toussaint, a well-known 45-year-old German art detective who has been hired by Goudstikker's daughter-in-law, Marei von Saher, a resident of Greenwich, Conn., to track down the rest of the collection. Finding looted art has been his business since the mid-1980's and, working on a contingency fee, he has scored some notable successes, including tracing five Malevich paintings to the Museum of Modern Art in New York. (The museum returned one to the heirs of Malevich and paid compensation for the others).