* Writes down value of GLG by $91 mln
* AUM fall to $52.7 bln at end-June from $59 bln at end-March
* Net outflows $1.4 bln over 3 months
* Adjusted pretax profit for 6 months to end-June $121 mln
LONDON, July 24 (Reuters) - Hedge fund manager Man Group plans to cut costs by a further $100 million a year, its first move under finance director Jonathan Sorrell to shore up profits in the face of dwindling sales.
The fund firm, whose shares have lost about three quarters of their value since the start of 2011 on the back of client outflows, has faced pressure to cut deeper or faster, and this is its third wave of savings since Man bought rival GLG in 2010.
The move could see hundreds more jobs among Man's roughly 1,500 workforce lost, following 400 job cuts already made.
"The steps we are taking today, by looking at costs ... (means we are positioned for) ... possible protracted and continued unstable markets," said chief executive Peter Clarke.
"Yes, gross margin has come down but costs have come down," he said on a telephone call to journalists.
By 1016 GMT Man's shares were up 9.3 percent at 75.5 pence.
Man also said on Tuesday that it had written down the value of fund manager GLG, a controversial $1.6 billion acquisition intended to reduce reliance on its flagship computer-driven fund AHL, by $91 million.
It also wrote down the value of its multi-manager business by $142 million.
The cost cuts, which bring savings since the GLG deal to $250 million, come as the former FTSE 100 company adjusts to falling assets and lower sales of high-margin guaranteed products, which have suffered from poor performance by AHL.
Clarke said some cuts would come in guaranteed products, a labour-intensive section of the business that runs highly complex products with a fixed term mixing a range of funds.
"The fact that guaranteed products are relatively high maintenance ... (means it) ... is a place where we can make savings," said Clarke. "We're not seeing a lot of demand."
The cuts are the latest step in a fightback signalled last month when Man replaced finance director Kevin Hayes with Jonathan Sorrell, son of WPP chief executive Martin Sorrell.
Man, which has been shedding assets since the credit crisis, apart from during the first six months of last year, said clients pulled out a net $1.4 billion over the three months to the end of June, largely from AHL and roughly in line with analyst forecasts.
Total assets under management (AUM) fell to $52.7 billion from $59 billion at the end of March.
"The number to focus on is the precipitous fall in the AUM over the past 12 months. This highlights the problem that Man faces - during times of uncertainty funds flow out of the door regardless of fund performance," said Peel Hunt analyst Mark Williamson, who says the stock is "uninvestable".
One of the big contributors to Man's woes has been the poor performance of AHL, which accounts for 70 percent or more of Man's earnings, according to broker Numis.
This $16.7 billion 'black box' fund, named AHL after 1980s founders Michael Adam, David Harding and Martin Lueck, lost 6.4 percent in 2011 and saw net outflows of $1.1 billion in the three months to June.
Clarke said on Tuesday that Nomura Global Trend, an open-ended version of AHL that had raised $2 billion by last May after a high-profile launch in Japan, had shrunk to about $800 million.
However, performance has picked up in recent months, thanks to short bets on oil and metals and long positions in U.S. Treasuries and UK gilts, helping it gain 4.5 percent between May 21 and July 16. So far this year the fund is up 1.1 percent.