Christie's, Sotheby's and smaller rivals like Phillips de Pury hold a three-week series of auctions featuring works by artists as diverse as Rembrandt, Renoir and Gerhard Richter.

Euro zone turmoil and slowing Chinese economic growth are giving investors the jitters, yet the high-end art market has defied gravity on a record-breaking streak.

New York has long been considered the global capital of the auction world -- most recent records have been set there, including the $120 million paid for Edvard Munch's "The Scream" at a Sotheby's sale in May.

London, a more natural fit for Russian tycoons who have homes in the city and Middle Eastern buyers just a mid-haul flight away, may be closing that gap.

Sotheby's has calculated that, while the number of lots sold to buyers from "new" markets has risen in both cities so far this year, the increase has been far more marked in London (33 percent) than New York (six percent).

"Particularly the Russians feel very comfortable bidding in the London sales as many of them have second homes and are very active here," said Helena Newman, chairman of Sotheby's impressionist and modern art department in Europe.

"I think that because of our geographic situation, we are the gateway to the East ... Central Asia, the Middle East and the East," she told Reuters at the company's London headquarters where star lots from the upcoming sales were on display.

"We definitely see that in the sales of recent years. It is a growing trend."

BILLION-DOLLAR BONANZA?

Beyond bragging rights, auctioneers are not overly concerned with who buys what where. Key lots for sale in London come from the United States, for example, and the market overall has become more globalised.

One of the prize lots of the season is English artist John Constable's "The Lock", being offered by Christie's for 20-25 million pounds and the only one of a series of six important landscapes by the painter to be in private hands.

It goes under the hammer on July 3 and should eclipse the 10.8 million pounds raised when it was sold in 1990 - a British painting record it held for 16 years.

On the same night, Rembrandt's "A Man in a Gorget and Cap" is on course to raise 8-12 million pounds.

On Wednesday, a Renoir nude is set to fetch 12-18 million pounds and the next week the same auctioneer offers Yves Klein's "Le Rose du Bleu", estimated at 17-20 million pounds and Francis Bacon's "Study For Self-Portrait" (1964) (15-20 million).

Christie's, the world's largest auction house, expects to raise at least 310 million pounds from its sales of impressionist, modern, contemporary art as well as those of British paintings and Old Masters.

The upper estimate is closer to 500 million pounds, and combined with Sotheby's low target of 210 million pounds, a billion-dollar art bonanza looks within reach.

"The four week summer season of major international auctions at Christie's ... is set to become one of the richest and most valuable series of auctions in company history," said Jussi Pylkkanen, head of Christie's Europe.

MIRO RECORD IN SIGHT

At Sotheby's, the top work of the season could be Joan Miro's "Peinture (Etoile Bleue), valued at 15-20 million pounds and in sight of the artist record set this year of 16.8 million.

Its appearance so soon after the February record is no coincidence -- auction houses tailor sales to reflect the latest tastes, and the Miro, along with works by Henry Moore and Surrealist Paul Delvaux, all follow recent auction highs.

The prominence of large, colourful, figurative works at Sotheby's, including Kees van Dongen's "Lailla", Marc Chagall's "L'Arbre de Jesse" and Delvaux's "Deux Femmes couchees", also reflects emerging market tastes.

Soaring prices for coveted works of 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 three years the market has defied the gloomiest predictions.

There has been weakening in Chinese demand 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 contraction was as much a reflection of sellers backing away as of falling demand, experts say, and auction houses believe they are back in a "virtuous cycle" of rising prices in turn attracting the very best works on to the market.

Institutional acquisitions have also 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.

Widespread reports said the Gulf state paid $250 million for Paul Cezanne's "The Card Players" in a private deal, believed to be the highest price ever paid for a work of art. (Reporting by Mike Collett-White, editing by Paul Casciato)

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