NEW YORK — Facing a still uncertain economy, the world's two leading auction houses head into their busy spring auction season with fewer artworks to sell and lower estimates than in previous years. But the picture isn't entirely grim.

Both Sotheby's and Christie's are featuring unusual pieces in May that haven't been on the market for decades. And even though many wealthy collectors have been hammered by the recession, there are still plenty of investors and art museums with the resources to spend millions of dollars on art.

"Sotheby's and Christie's have done a very good job of getting property consigned at realistic estimates" considering current market conditions, said David Nash of the Manhattan gallery Mitchell-Innes & Nash, who is an expert in impressionist and modern art. "They've edited these sales quite well, and kept them short."

On Tuesday, Sotheby's is offering 36 impressionist and modern works in an evening sale that is traditionally reserved for its best merchandise. The sale is expected to bring up to $118.8 million, compared to last spring, when 52 lots sold for $235.4 million.

Christie's has 50 lots at its evening sale on Wednesday, which it expects will bring $94 million. Last spring it had 58 works, and realized $277.2 million for 44 sold lots.

Both houses are offering exceptional works by Pablo Picasso, Alberto Giacometti, Max Ernst, Piet Mondrian and David Hockney, but there are fewer star-quality works because "sellers are reluctant to sell to this market because they don't think they will get the best price," Nash said.

While few world records are expected to be set at the auctions, both houses are offering works that boast impeccable provenance and are fresh to the market.

Christie's has a 1971 Picasso, "Woman With Hat," belonging to film director Julian Schnabel, who has consigned it to help finance a real estate project.

Showing a female figure with a face reminiscent of the artist himself, the canvas is expected to sell for $8 million to $12 million. Picasso himself selected the canvas for a solo exhibition in Avignon, France, in 1973, but he died a month before it opened.

At Sotheby's, an important Giacometti work, "The Cat" (estimated at $16 million to $24 million), was last seen at auction in 1975. And an abstract painting by Mondrian, "Composition in Black and White, With Double Lines" ($3 million to $5 million), has been on loan since 1967 at the Dallas Museum of Art.

Another Picasso with stellar provenance is being sold at Sotheby's: "The Daughter of the Artist at 2 1/2 With a Boat," a 1938 painting estimated to sell for $16 million to $24 million. It remained in the artist's possession until his death, and a private collector has owned it since the 1980s.

Among several works never seen at auction is "A Curse on You Mothers," a massive Ernst oil of birdlike human forms. Estimated to sell for $7 million to $9 million at Christie's, it could break the current record for an Ernst painting of $2.4 million, set in 2008 for his "The Conversion of Fire."

Both houses are also offering property from well-known private estates. Christie's has three works by Giacometti, Henry Matisse and Joan Miro belonging to Caral G. Lebworth of Gimbels department store fame. All three represent pivotal points in the artists' careers and have never been to auction: Giacometti's "Bust of Diego" ($4.5 million to $6.5 million), Matisse's "Nude With a White Towel" ($2 million to $3 million) and Miro's "Study for Figure" ($300,000 to $400,00).

Sotheby's has two works by Camille Pissarro and one by Claude Monet from the collection of Louisine and Henry Osborne Havemeyer, whose many works were gifted to the Metropolitan Museum of Art. For its May 13 contemporary sale, Christie's has high hopes for 19 paintings that belonged to the late art patron Betty Freeman.

But Nash said the sales also contain a number of works that failed to sell at recent auctions, such as Marc Chagall's "The Event" at Christie's in November 2007. It was estimated at $5 million to $7 million, and is now being reoffered for a lower $3 million to $4 million estimate.

Guy Bennett, Christie's international co-head for the impressionist and modern department, said the auction house's upcoming impressionist sale "is made up of items at all price points because it's important to recognize that the market has shifted significantly."