(Corrects fall in broader market in final graf)

* Woolworths FY net profit down 12.5 pct, revenue flat

* Gordon Cairns to replace Ralph Waters as chairman

* Food and liquor sales down 0.9 pct in first 8 weeks of current year

SYDNEY, Aug 28 (Reuters) - Australian supermarket chain Woolworths Ltd appointed a new chairman on Thursday as it reported its first fall in full-year net profit in at least 19 years amid tough competition and falling market share.

The country's biggest supermarket operator said former Lion Nathan chief executive Gordon Cairns would replace Ralph Waters as chairman. Waters will step down next week, following chief executive Grant O'Brien out the door after the 91-year-old company's horror year.

Net profit for the year ended June 28 fell 12.5 percent to A$2.15 billion ($1.54 billion). The result was in line with a shock profit warning issued by the company in June when it announced O'Brien's departure - its second warning in four months.

Revenue was flat at A$61.15 billion, while the company took A$426 million of one-off costs and writedowns associated with a restructuring.

The retailer also revealed sales in its key food and liquor division declined 0.9 percent in the first eight weeks of the current year.

Woolworths' leadership team has faced intense scrutiny after ceding market share to arch-rival Coles, owned by Wesfarmers Ltd , and cut-price newcomers like Germany's Aldi , leading to its first quarterly sales decline in more than 20 years in the third quarter.

The company's fortunes contrast with Wesfarmers, which last week reported an 8.3 percent rise in full-year net profit to A$2.44 billion.

Woolworths Food Group Managing Director, Brad Banducci, said the company had advantages in scale and its supply chain, but warned that margins would continue to be hit.

"A more competitive environment will result in lower margins as we invest to improve all aspects of the customer experience, notwithstanding gathering momentum in operating efficiencies," Banducci said in a statement.

Woolworths has launched a global search to replace O'Brien, who will retain his role until a successor is appointed. Cairns, who was also chairman of David Jones for five months before its sale to South Africa's Woolworths, will replace Waters on Sept. 1.

The company announced a final dividend of 72 Australian cents per share.

Woolworths shares have slumped 26 percent over the past year, compared with a 7.4 percent fall on the broader market. The stock last closed at A$27.05 on Thursday.

($1 = 1.3945 Australian dollars) (Reporting by Jane Wardell; Editing by Richard Pullin)