One of the winners in the administration's proposal to reduce farm price supports could be the futures industry.

At a briefing for reporters yesterday, John Damgard, president of the Futures Industry Association, hailed the idea of ending crop subsidies, while recognizing the need for a transition period as well as a safety net. "I compliment Mr. Block and Mr. Stockman," he said, referring to Agriculture Secretary John Block and David A. Stockman, director of the Office of Management and Budget, who formed the plan.

The goal is to reduce the $12.9 billion estimated cost of subsidies in fiscal 1987 to about half that by fiscal 1990. This would be done by reducing the target price to farmers and cutting the level of price-support loans on major crops.

Allowing crop prices to be determined by the law of supply and demand rather than dictated by Washington would increase the volatility of prices. To hedge against uncertainty, farmers and others involved in the food chain would be more likely to use the futures markets.

A futures contract obliges the buyer to buy or sell a commodity at a specified price by a fixed date. Futures are used by hedgers to protect their investments as well as by speculators to make money.

Falling commodity prices and low inflation have seriously affected agricultural futures. The number of contracts traded last month dropped to 3.5 million from 5.2 million in November 1983. For the 11 months of this year, futures on agricultural products dipped to 46 million contracts from 59 million in the same period of 1983. The decline has resulted in a number of failures and mergers in the commodities business.

Trading in precious and other metals and lumber products has declined this year. On the other hand, there were significant gains in foreign currency, petroleum products, financial instruments and stock indices trading. In fact, the volume of financial futures -- from Treasury bonds to German marks to the Standard & Poor's 500 index -- now exceeds that of traditional physical commodities such as soybeans and pork bellies.

Trading in crude oil contracts has risen dramatically to 1.6 million contracts from 225,000 last year. FIA officials explained that petroleum companies, which for some time ignored the futures market, have now found it necessary in view of declining prices.

Damgard spoke optimistically of prospective links with futures markets in Hong Kong and Tokyo along the lines of the Chicago-Singapore link set up last fall to extend the trading day by following the sun. However, he admitted that trading was still disappointingly small.

"People just aren't worrying about trading D-marks at 3 a.m.," said John J. Conheeney, chairman of Merrill Lynch Futures.

Just this week an options exchange in Sydney, Australia, announced its plan to hook up with exchanges in Vancouver and Montreal and the European Options Exchange in Amsterdam.