UPDATE 2-Vodacom sees H1 profit down due to impairment charge

* Sees H1 headline EPS 10-20 percent lower

* Expects impairment losses of 3.2 billion rand

* Shares down 4 percent

(Adds detail, analyst comment, shares)

By Serena Chaudhry

JOHANNESBURG, Oct 20 (Reuters) - South Africa's biggest mobile operator Vodacom (VODJ.J) expects to post a drop in first-half profit, mainly due to a 3.2 billion rand ($438 million) impairment charge arising from an acquisition.

Vodacom, majority-owned by Britain's Vodafone (VOD.L), said on Tuesday it expected headline earnings per share --- the main profit gauge in South Africa -- for the six months to end-September to be 10-20 percent lower than the corresponding six months last year.

It said headline earnings had been hit by impairment losses relating to its acquisition of Gateway, where trading was poor due to increased price competition and tough economic conditions.

"The big one was that they've impaired Gateway by 3.2 billion rand... The concerning thing there is that they purchased this asset less than a year ago, and within nine months they've now impaired it by more than half," said David Lerche, a telecoms analyst at Avior Research.

Shares in Vodacom, which made a strong debut on the Johannesburg Stock Exchange in May, fell 3.93 percent to 53.32 rand by 0825 GMT, lagging a slightly firmer JSE Top-40 index .JTOPI of blue chips. Traders said the trading update had been worse than anticipated.

DRC BUSINESS HIT

Vodacom said headline earnings had also been hit by the reversal of a deferred taxation asset of about 500 million rand due to the reduced profitability of its business in the Democratic Republic of Congo (DRC).

"If you're writing off deferred tax assets, it means you are not expecting to make a profit. That says that the margins in DRC have just dropped dramatically," said Avior's Lerche.

"The DRC is Vodacom's biggest possible expansion area, just because of the large population there, so if we're not seeing growth in that large market, it's rather negative for Vodacom."

Vodacom Congo was established in December 2001. Vodacom owns 51 percent of the firm, while Congolese Wireless Network holds the remaining 49 percent stake.

Vodacom said group basic earnings per share were seen to be between 95-105 percent lower, while revenue is expected to rise by around 10 percent.

The mobile operator is expected to release its interim results on November 9. ($1=7.302 Rand) (Editing by Mike Nesbit)