* Results-based optimism overshadowed by U.S. caution

* Materials offset gains in other sectors

* BHP falls sharply after H1 results

By Aaron Saldanha

Feb 21 - Australian shares slipped on Wednesday as nervousness spilling over from U.S. markets overshadowed positive earnings news from many domestic companies, while index heavyweight BHP fell hard after reporting its half-year results on Tuesday.

The Dow Jones Industrial Average (.DJI) and S&P 500 (.SPX) fell on Tuesday to snap a six-session winning streak as a sharp decline in Walmart (WMT.N) weighed heavily, and the U.S. dollar touched to a six-day high, helped by U.S. Treasury yields which rose due to government bond auctions this week. (USD/) (US/)

"We got a nervous lead from U.S. markets and that was reflected not only in the drop in equity prices, but also in the fact that the U.S. dollar rallied," said Ric Spooner, chief market strategist at CMC Markets.

A stronger U.S. dollar tends to push down the price of commodities, of which Australia is a major exporter.

Australia's S&P/ASX 200 index (.AXJO) fell 0.1 percent, or 3.9 points on Tuesday to 5,937 by 0014 GMT. The benchmark was flat on Tuesday.

The losses among materials (.AXMM) and the main index were largely attributable to global miner BHP (BHP.AX) , which fell as much as 5.3 percent after reporting half-year results on Tuesday.

Peer Rio Tinto Ltd (RIO.AX) lost as much as 1.9 percent and was on track to end lower for a third straight session.

On the whole, the materials index was trading at the lowest in a week, losing as much as 3.1 percent. London Metal Exchange-traded copper and aluminium edged lower on Tuesday. (MET/L)

The Australian benchmark's top loser was software solutions provider WiseTech Global Ltd (WTC.AX) , despite an 8 percent rise in its half-year net profit.

On the other hand, Australia-listed shares of a2 Milk Company Ltd (A2M.AX) zoomed 23.4 percent after first half profit hit a record thanks to higher demand in China.

CMC Markets' Spooner said positive results like a2 Milk were "helping to balance out the extent of declines we have seen."

Energy stocks (.AXEJ) rose as oil prices hit their highest in nearly two weeks on Tuesday, as inventories declined. (O/R)

Resources-related engineering firm WorleyParsons Ltd (WOR.AX) jumped as much as 4.9 percent, the most since October, after reporting a profit for the first half.

Meanwhile, consumer staples stocks lifting the benchmark were the predominant theme in New Zealand trade.

New Zealand's S&P/NZX 50 index (.NZ50) rose 1.4 percent, or 113.64 points, to 8,211.91.

Shares of a2 Milk Company Ltd (ATM.NZ) jumped in their home country, as well. They were up as much as 24.8 percent to an all-time high.