Undated (AP) _ Precious metal futures prices fell back Thursday as a stronger dollar prompted selling that wiped out most of the sharp gains posted a day earlier.

On other commodity markets, copper futures also fell; oil futures retreated; grains and soybeans were mixed; and livestock and meat futures were mixed.

On New York's Commodity Exchange, gold for April delivery fell $2.50 to $337.20 a troy ounce; May silver tumbled 6.7 cents to $3.878 a troy ounce.

July platinum fell $1.20 to $368.10 a troy ounce on the New York Mercantile Exchange.

The losses in gold and silver wiped out Wednesday's advances. Platinum, which rose $6.90 on Wednesday, retained most of that gain amid uneasiness about political and racial tensions in South Africa.

Wednesday's surge in precious metal prices was triggered by violence in South Africa, the world's biggest platinum producer.

John O'Connell, metals analyst with the commodities brokerage firm Refco Inc., said the lack of follow-through buying Thursday left the markets vulnerable to profit-taking. He said the selling began about two hours after the markets opened, when the dollar rallied on international currency markets.

A stronger dollar makes U.S. goods costlier overseas, which reduces the likelihood of inflation and makes precious metals less attractive to investors.

The gold market failed a key test of the bullish attitude that has been building in the market this month following a strong rally on March 30, said Martin Reichenberg, director of trading services for the Pegasus Econometric Group in Hoboken, N.J.

''The psychology today almost completely reversed in the metals,'' he said.

He said the gold and silver markets ''are sort of tottering on the edge of falling back down to the levels we saw two weeks ago.''

Copper futures also fell sharply, reflecting a continuing lack of Far Eastern demand. April copper dropped 1.20 cents to 87.10 cents a pound on the Commodity Exchange.

In energy trading on the New York Mercantile Exchange, light sweet crude oil for May delivery fell 18 cents to $20.22 a barrel; May heating oil fell .09 cent to 55.92 cents a gallon; May unleaded gasoline slipped .03 cent to 60.43 cents a gallon; May natural gas fell 0.7 cent to $2.357 per 1,000 cubic feet.

Wheat for May delivery rose 5 3/4 cents to $3.55 1/2 a bushel on the Chicago Board of Trade; May corn rose 3/4 cent to $2.31 3/4 a bushel; May oats rose 3 cents to $1.47 3/4 a bushel; May soybeans fell 4 3/4 cents to $5.90 1/2 a bushel.

Livestock and meat futures ended mostly lower on the Chicago Mercantile Exchange.

Live cattle for April delivery fell .32 cent to 81.90 cents a pound; April feeder cattle slipped .05 cent to 85.60 cents a pound; April live hogs fell .43 cent to 47.07 cents a pound; May frozen pork bellies fell 1.78 cents to 51.17 cents a pound.