Auctioneers are pinning their hopes on "uber-collectors" to help London summer art sales top last year's $1 billion total when the series kicks off later this month.

Estimates from Christie's, Sotheby's and smaller rivals such as Phillips and Bonhams for sales over the next few weeks in the British capital show that the paintings, sculptures and furniture under the hammer are on course to defy a sluggish global economy again this year.

The top two houses have put more than $300 million worth of their most expensive works up for sale on public show until June 11 at their London galleries in Mayfair, hoping pre-sale exhibitions might inspire a bit of impulse-buying from serious collectors making the London stop on the art trail.

"What we hope is that the rather more transitory uber-collectors who are in London, Basel and Venice will come in and see things that they wouldn't normally look at," deputy chairman of Christie's Europe, Orlando Rock, told Reuters.

Christie's, the world's biggest auctioneers, has a star lot that is a price-on-request (around $23 million) diptych by 20th century American painter Jean-Michel Basquiat, and a painting from Russian Expressionist Wassily Kandinsky, which could set a lifetime record for the artist if it sells north of $23 million. Its top estimate is $24.86 million.

Nearest rival Sotheby's has French Impressionist Claude Monet's "Le Palais Contarini" with a top estimate of $31 million and paintings by 18th century Frenchman Claude-Joseph Vernet ($7.7 million) and British contemporary artist David Hockney ($4.6 million).

Continued weakness in a battered euro zone and slowing Chinese economic growth have made investors wary in the last two years, but high-end art sales have continued to break records.

New York has long been considered the global capital of the auction world - most recent records have been set there.

This year's spring auctions were no different, ending on a record-shattering high as Christie's May 15 post-war & contemporary art sale achieved the highest total - $495 million - in the history of art auctions.

None of the star London lots currently come near the $58.4 million paid at the Christie's sale in New York for U.S. artist Jackson Pollock's "Number 19, 1948".

SILKWORM

A closer look at the estimates from Christie's and Sotheby's give a mixed picture of a London season that looks healthy but may not blast the record books.

Estimates from Christie's of about $388 million for this year are lower than sales of just under $600 million last year, although the top estimate from Sotheby's for $562 million easily eclipses last year's nearly $385 million.

Alongside the Old Masters, modern and fine art, auction houses have mixed in precious objects such as a Georgian coffee pot expected to become the most expensive piece of English silver ever sold and a 15th century Virgil manuscript, as well as collectibles like a watch worn by James Bond in "Thunderball" and unreleased lyrics from singer Bob Dylan.

London, a natural fit for Russian tycoons who have homes in the city and Middle Eastern buyers just a mid-haul flight away, will offer sought-after sculptures from antiquities to Alberto Giacometti, Henry Moore and Elisabeth Frink, as well as fine Louis XIV furniture.

A jeweled automaton silkworm lurks near a pair of Louis XVI vases among the 80 works chosen by Sotheby's for public display, along with a 17th century El Greco painting and a 1927 piece from Dutch painter Piet Mondrian.

"This will be an exhibition that speaks to the catholic taste of today's collectors as well as to everyone who loves great works of art and enjoys the thrill of the unexpected," said Mario Tavella, Sotheby's deputy chairman for Europe.

Soaring prices for art at a time of global economic uncertainty have long prompted warnings of a sharp correction and even collapse, but time and again in the last four years the market has defied the gloomiest predictions.

Chinese demand has weakened and tastes can be fickle, but the very best works of art have generally risen in value since a sharp but brief drop in auction turnover in 2009.

The only copy of Edvard Munch's seminal image "The Scream" still in private hands came up for sale at Sotheby's in New York last year.

After nearly 15 minutes of intense bidding, made in million-dollar increments, it sold for $120 million including commission, a new auction record for any work of art.

The two previous records were also recent - Pablo Picasso's "Nude, Green Leaves and Bust" fetched $106.5 million in 2010, having sold for $19,800 in 1951. In the same year Giacometti's "Walking Man I" made $104.3 million.

Institutions have played a key role in the recovery, with Qatar emerging as one of the biggest buyers of art in recent years as it fills a growing network of museums.

According to widespread reports, the Gulf state paid $250 million for Paul Cezanne's "The Card Players" in a private deal in 2011, which is believed to be the highest price ever paid for a work of art.