South African stocks slip ahead of long weekend

* Top (Taiwan OTC: 8419.TWO - news) -40 index slips 0.1 percent at 38537.55

* All-share index down 0.15 percent at 43185.73

JOHANNESBURG, Dec 13 (Reuters) - South African stocks edged down on Friday, falling for the fourth straight trading day as concern intensified the U.S. Federal Reserve could start scaling back its stimulus as early as next week.

Shares of blue chip companies such as Impala Platinum (Other OTC: IMPUY - news) and Assore were among the decliners, a day after the Johannesburg bourse suffered its biggest daily drop in almost six months and ahead of a long weekend that includes a national holiday on Monday.

Investors are worried the U.S. Federal Reserve will begin scaling back, or tapering, its massive bond-buying stimulus programme that has underpinned equities in emerging markets such as South Africa.

"There is a bit of holiday selling coming in now, we have the Fed meeting next week, so the talk of tapering seems to be the word of the day," said Brandon Sacks, a sales trader at Avior Research in Johannesburg.

"I think guys are sitting back waiting for that to happen, yesterday was the start of it."

The benchmark Top-40 index ended the session 0.1 percent lower at 38,537.55, while the broader All-Share (LSE: SHRE.L - news) index slipped 0.15 percent at 43,185.73.

Impala Platinum fell 2 percent to 109.19 rand while Assore dropped 3.3 percent to 342.27.

Shares in Adcock Ingram hardly moved after the news that Chilean drugmaker CFR Pharmaceuticals sweetened its cash and stock takeover offer for Adcock by 1.6 percent to 12.8 billion rand ($1.23 billion).

CFR Pharmaceuticals upped its offer in an attempt to fend off a rival bid from a local Bidvest and also win approval from Adcock's top shareholder, South African state pension fund, the Public Investment Corporation.

Shares of Anglo American Platinum dropped 0.6 percent to 363.73 rand. Mining (LSE: MIR.L - news) union AMCU increased its membership at the world's top producer of the metal, by 50 percent in the last five months and now represents 60 percent of shaft workers.

Trade was relatively slow, with 188 million shares changing hands, with 173 decliners and 123 advancers. A total of 54 shares remained unchanged.