The final item of the most valuable single-owner collection ever auctioned went under the hammer at Sotheby's today, bringing the grand total for the dispersal of the possessions of the late Florence J. Gould to $48.6 million.

The total -- the sum of four auctions of the late expatriate's jewelry, furnishings and artwork held at Christie's and Sotheby's over the past year -- toppled the previous record of $34.2 million in 1978 for the collection of the late Robert von Hirsch.

"I've been living with this Gould sale for so long," John Marion, president of Sotheby's and today's auctioneer, said after the sale, " . . .in some ways all I can think is this is a relief."

Since the widow of Frank Gould, the youngest son of railroad tycoon Jay Gould, died in 1983 in Cannes, selling her things has been a lot of work. Last April her jewelry sold for a record $8.1 million at Christie's in New York. Last June Sotheby's auctioned her French furniture in the Sporting d'Hiver in Monte Carlo for $6.5 million.

Wednesday night thousands of well-heeled art collectors thronged Sotheby's salesroom here and witnessed a record $9.9 million Vincent van Gogh painting change hands. "Paysage au Soleil Levant" and 55 other French Impressionist and post-Impressionist artwork racked up $32.6 million in sales.

Compared with the other three Gould sales, today's was a quiet wind-down. About 100 casually dressed art fanciers bid a total of $1.3 million for 123 paintings, drawings and prints. The top price was a seemingly modest $148,500, paid by an unidentified buyer for Sir Henry Raeburn's circa 1817 "Portrait of Master William Blair of Abontoun."

Number two in today's art price contest went to a landscape attributed to Jean-Honore Fragonard. "The Grand Staircase of the Villa D'Este at Tivoli" was bought by an unidentified New York dealer for $132,000. The remaining pictures, including 32 drawings and paintings by Gould's personal friend Max Jacob, each sold for under $100,000.

When Florence Gould died, the childless widow's will stipulated that all her possessions be liquidated. The recipient of the proceeds is the Florence J. Gould Foundation, set up to benefit Franco-American amity. As of today the trustees have not figured out exactly how the money will be spent, although some of it will go to literary prizes for French writers and research for American scholars of French art.

But John Young, Gould's executor and head of the foundation, made one thing clear: "Don't write that we don't know what to do with the money," he said after the sale. "We've already been besieged with offers. Everyone seems to know how it should be best spent."