* Retail sales up 38 pct in 4 months to Dec. 31
* UK sales up 37 pct, international sales up 38 pct
* Retail gross margin up 90 basis points
* CEO comfortable with FY profit forecasts of 71 mln stg
* Shares fall as much as 6.1 pct
By James Davey
LONDON, Jan 14 (Reuters) - British online fashion retailerASOS said growth slowed in the United States andAustralia, two key markets, taking the shine off a big jump inChristmas sales.
ASOS, founded in 2000 by current chief executive NickRobertson, has been a success story in British retailing withits fast-changing fashions appealing to internet-savvytwentysomethings and attracting fans including U.S. First LadyMichelle Obama and singer Rita Ora.
Its shares have more than doubled over the last year, givingit a market value of 5.8 billion pounds ($9.5 billion), only 2billion pounds less than the 130 year-old Marks & Spencer, Britain's biggest clothing retailer.
However, that high valuation gives ASOS little margin forerror and its shares fell as much as 6.1 percent on Tuesdayafter the company posted sales figures for the first four monthsof its 2013-14 financial year.
"Though the impressive UK outcome should certainly be seenas reassuring, some people will be fretting about the overseasslowdown," independent retail analyst Nick Bubb said.
ASOS said retail sales rose 38 percent to 335.7 millionpounds in the four months to Dec. 31, as the firm cashed in onthe big trends of oversized coats, slip dresses and the vinyl,pvc and patent leather look.
That compares with analysts' consensus forecast for growthof 36 percent and 47 percent growth in the fourth quarter of its2012-13 year.
ASOS's UK sales jumped 37 percent to 133.7 million pounds,with international sales up 38 percent to 202 million pounds.
Sales in Europe were particularly strong with growth of 69percent. However growth in the U.S. slowed to 28 percent from 59percent in the previous three months, reflecting a toughermarket for clothes aimed at young people.
In ASOS's 2012-13 year, the U.S. contributed about 10percent of total sales.
"We think we can do better in the U.S., time will tell,"Robertson said.
Growth in ASOS's Rest of World (RoW) division, whichincludes Australia, Russia and China, slowed to 19 percent from26 percent.
Robertson said the segment was being dragged down byAustralia, where the local currency has strengthened against thepound.
"On a like-for-like basis because of the Australian dollarwe are about 15 percent more expensive than we were this timelast year," he said.
RoW accounted for about 30 percent of total sales last year.ASOS does not break down the performance of individual countriesin this segment.
SHIFT ONLINE
ASOS said the retail gross margin rose 90 basis pointsyear-on-year in the period, reflecting tighter stock control.
Industry data published on Thursday showed that while totalUK retail sales were up 1.8 percent year-on-year in December,online sales of non-food products grew 19.2 percent, reflectingthe speed of the shift in demand from physical stores to theInternet.
Robertson said ASOS's results were also driven by the firmoffering better delivery options, such as a next-day servicewith hourly slots in the UK, and additional payment methods.
Some analysts are concerned about a potential rise inreturned purchases and the cost of delivering goods more quicklyto ever more demanding shoppers.
Robertson, however, was relaxed. "You've got to rememberthis is all we do. I'm not trying to juggle investment across astore portfolio and this. Our investment only goes in one placeand that's improving the speed and efficiency of gettingcustomers their orders."
He said the company was on track to make 1 billion pounds ofsales in the 2013-14 year, one year ahead of target, and iscomfortable with analysts' consensus forecast for underlyingpretax profit of 71 million pounds, up from 54.7 million poundsin 2012-13.
Marks & Spencer (MKS)