NEW YORK (REUTERS).- One of the most valuable private art collections ever offered at auction, led by an $80 million Picasso, will be sold in May in a sign that the art market might soon flirt with the record levels seen before the financial crisis struck in 2008.

The sale of more than 50 works at Christie's from the estate of Mrs. Sidney Brody, a Los Angeles philanthropist who died in November, is conservatively estimated to sell for more than $150 million.

It is one of two prestigious collections being handled by Christie's. The other collection includes 100 works owned by late best-selling writer and director, Michael Crichton.

"This is one of the more remarkable collections of its kind in this country," Christopher Burge, Christie's International honorary chairman said as the works went on public display.

The star of the Brodys' modern art collection, most of which was assembled during the 1950s, is Picasso's "Nude, Green Leaves and Bust," a pristine, vibrant large-scale portrait of Picasso's mistress, Marie-Therese Walter from 1932.

It was the couple's first Picasso, acquired directly from his dealer in 1951 for $19,800. It has not been seen publicly in nearly 50 years.

Christie's estimates the work will sell for about $70 million to $90 million, which would achieve one of the top prices for art at auction. Picasso's "Boy with a Pipe" sold for $104.1 million in 2004 and "Dora Maar with Cat" fetched just over $95 million in 2006.

The art world was electrified in February when a Giacometti bronze "Walking Man, I" soared to $104.3 million and rekindled hopes that prices for rarely available, top-quality works of art could potentially reach stratospheric levels.

Giacometti's "Grande tete de Diego," estimated at $25 million to $35 million, and a Matisse nude expected to sell for up to $30 million, are other highlights.

The centerpiece of the Crichton collection is one of Jasper Johns seminal "Flag" works, created from 1960 to 1966, which the best-selling author of "Jurassic Park" and creator of the hit television series "ER" acquired from the artist in 1973. He kept it in his bedroom until his death in 2008.

Crichton did not consider himself a serious collector, once writing, "I just bought images that I enjoyed looking at."

But Brett Gorvy, Christie's Americas deputy chairman, said he was "very, very knowledgeable as a collector," if extremely private and low-key about it.

Crichton was also close friends with Johns, and the iconic "Flag," one of the artist's few works to be auctioned in the past decade, is "emblematic of their relationship," Gorvy said.

Estimated at $10 million to $15 million, Christie's said it was priced conservatively in view of a still-recalibrating market. An earlier Johns flag reportedly sold for around $110 million on the private market.

The Crichton collection, which also features works by Picasso, Andy Warhol and Roy Lichtensteins, is expected to sell for $50 million to $75 million, although competition for such prestigious private collections often sends prices far above expectations.

(Editing by Patricia Reaney)