LONDON, Sept 24 (Reuters) - British retailer Marks & Spencer (MKS.L) is expected to report, at best, a slight improvement in its sales trend during its second quarter, as the debate over the successor to executive chairman Stuart Rose rumbles on.

M&S, which sells clothes, homewares and food from over 600 stores in Britain and 285 abroad, is forecast to report sales at British stores open at least a year fell 1.4 percent in the three months to end-September, according to the consensus forecast in a poll of 10 analysts provided by the company.

Forecasts for the fall in M&S's second-quarter sales were in a 0.5-2.2 percent range. A 1.4 percent outcome would be unchanged from the fall reported for the first quarter of M&S's 2009-10 year and would represent an eighth successive quarterly fall in sales.

Like-for-like general merchandise sales, spanning clothing and homewares, were expected to have fallen 1-4 percent, having been down 2.4 percent in the first quarter.

Food sales on the same basis were seen in a range of down 1 percent to up 0.5 percent, having fallen 0.5 percent in the previous quarter.

That food performance would still look poor compared with recent updates from rivals such as John Lewis's [JLP.UL] Waitrose which has been the fastest growing British supermarket over the past three months.

"M&S continues to underperform the market in both clothing and food, and until we see initiatives likely to close this gap, we continue to prefer other retail shares," said analysts at Deutsche Bank.

RESILIENT ROSE

In July, Rose saw off a second investor rebellion in as many years over his elevation from chief executive in contravention of corporate governance guidelines. The board's position on succession is that it will appoint a new chief executive next year and Rose will step down as chairman by July 2011.

Some investors think it unwise for Rose to remain chairman after a new CEO is appointed, while others do not share his preference for an internal candidate to succeed him as CEO.

After slumping in 2008, M&S shares have risen by 65 percent over the past year on recovery hopes, outperforming the DJ Stoxx European retail index .SXRP by 42 percent.

Analysts forecast a 2009-10 pretax profit of 540 million pounds, according to a company poll, down from 604 million in the previous year.

Some analysts expected M&S to raise its full-year gross margin guidance, which stands at a fall of 125-175 basis points, due to reduced promotional activity in the market and improved stock control.

Recent updates from rivals, such as Next (NXT.L), have exceeded expectations but mid-market players are continuing to trail the likes of budget player Primark (ABF.L) as the recession drags on.

Fast-growing online fashion retailer ASOS (ASOS.L) will also publish a trading update on Wednesday 23 September.

The company, which targets internet-savvy 18 to 34 years old looking to emulate the desginer looks of celebrities such as Kate Moss at a fraction of the price, reported a 52 percent rise in sales in the 13 weeks to June 26, down from the 104 percent growth for the year ended March 31.

Analysts expected the slower growth rate to continue, but said the introduction of free returns in Britain earlier this month could give a boost heading into Christmas trading. (Additional reporting by Mark Potter; Editing by Dan Lalor)