Auction houses are guaranteeing prices of some top works in this week's London art sales, which coincide with the worst financial crisis since the Depression.

The sales, which take place at the same time as the Frieze Art Fair, have a total minimum price tag of 107 million pounds ($187 million). Sotheby's has more than half of its total lot value guaranteed; Christie's International guarantees 38 percent, meaning both promise fixed prices to vendors whether the art sells or not.

``I'm concerned about the level of guarantees at these auctions,'' said London dealer Gerard Faggionato. ``I just can't see people wanting to spend 12 million pounds on a work of art at the moment.''

The auctions starting Oct. 17 pose additional risks to auction houses as banks are bailed out and economic gloom prevails. A survey of U.K. valuers said the Damien Hirst sale last month might have marked the top of the art market.

``Everything appears to be on hold at the moment,'' said the London-based art adviser Tania Buckrell Pos, who represents high- net-worth clients in both the developed and emerging economies. ``Everyone has a budget, even if they're a billionaire. These people know when to be prudent. At this time, some of my clients are balancing the decision to buy art against other assets.''

In June, Buckrell Pos paid a record 40.9 million pounds with fees at Christie's in London for Monet's 1919 painting ``Le Bassin aux Nympheas.''

`Changed Mood'

``The mood has changed over the last couple of weeks,'' said Anders Petterson, founder and managing director of the London- based art market research company ArtTactic. ``The magnitude of the economic crisis is such that even the ultra-rich will have second thoughts about buying things.''

New York-based Sotheby's said its Oct. 17 contemporary-art sale is expected to fetch at least 30.6 million pounds from 64 lots. According to the catalog, Sotheby's has guaranteed or has a financial interest in 10 works with a combined low-end estimate of 15.45 million pounds.

The seller of Andy Warhol's 10-panel 1976 ``Skulls,'' estimated at 5 million pounds to 7 million pounds, has been promised a minimum price, as have the consignors of Gerhard Richter's figurative landscape, ``Jerusalem,'' and the same artist's ``Abstraktes Bild (Rot),'' which are expected to fetch at least 5 million pounds and 3 million pounds respectively.

10-Skull Warhol

``We guarantee the works we believe in,'' said Cheyenne Westphal, Sotheby's European chairman of contemporary art, in a phone interview. ``The 10-skull Warhol is a really exceptional, possibly unique piece.''

Over the last 12 months, Sotheby's shares have lost 77 percent of their value. The stock closed at $12.25 yesterday.

Christie's Oct. 19 sale in London includes a black egg-shaped ``Fine di Dio'' canvas by Lucio Fontana with a lower estimate of 12 million pounds. The valuation is 1.7 million pounds more than the artist's auction record. The seller of this 1963 work -- the only lot of the week to carry an eight-figure estimate -- has been guaranteed a minimum price, said Christie's.

In June, a pink ``Fine di Dio'' valued at 8 million pounds failed to sell at Christie's. Three years earlier, another pink example sold at Sotheby's London for 1 million pounds with fees, according to Artnet.

Expected by Christie's to fetch at least 57.8 million pounds, the 48-lot auction features five other works with guarantees, including a Francis Bacon portrait of his friend Henrietta Moraes with a low estimate of 5.5 million pounds. The total amount of guaranteed works comes to 22.1 million pounds.

`Good Feedback'

``We've just toured the material to Europe and the States, and the feedback was very good,'' said Pilar Ordovas, Christie's head of contemporary art in London. ``We feel what we're offering is high quality, fresh to the market and correctly estimated.''

Ordovas said that if necessary the reserve prices of lots could be lowered to make them more attractive to buyers. ``As usual, if we feel we need some room, we'll talk to our sellers.''

Phillips de Pury, which has just been acquired by the Moscow- based Mercury Group, said it has not put a guarantee on the 23- foot high Takashi Murakami sculpture, ``Tongari-kun,'' that leads its Oct. 18 evening auction with an estimate of 3.5 million pounds to 4.5 million pounds. The 70-lot auction has an overall estimate of 18.5 million to 26 million pounds.

``In the past, people have said that if Western collectors buy less at auction the market will be supported instead by buyers from the emerging economies,'' said Petterson. ``I'm not so sure now.''

Richest Russians

The combined wealth of Forbes magazine's 25 richest Russians tumbled 62 percent between May and October, based on the equity value of traded companies and analysts' estimates of closely held assets they own.

Sotheby's five-day October series of auctions of Chinese art and jewelry in Hong Kong achieved only half its expected total. Christie's Oct. 7 sale in London of Islamic and Indian art found buyers for only 47 per cent of the lots.

``There's an awful lot riding on these sales in London and next month in New York,'' said the London dealer Alan Hobart. ``If they're successful, confidence in the art market will be maintained. If not, people will pull out very quickly.''