There'll be yet another new game for investors to play this summer, if plans unveiled by an affiliate of the American Stock Exchange are approved.

Officials of Amex and its subsidiary, American Commodity Exchange, plan to present a proposal today for the trading of futures contracts in Government National Mortgage Association certificates to the Commodity Futures Trading Commission.

The move will bring the new exchange head-to-head with the powerful Chicago Board of Trade over which city will attract the mega-bucks investments in financial instruments. The Board of Trade, whose members trade GNMA futures and other money market instruments as well as agricultural commodities and metals, is the largest of the nation's eleven commodity exchanges.

Amex Chairman Arthur Levitt Jr. told a news conference in New York Friday that "New York City is a natural location" for the proposed GNMA market. He noted that a majority of the members of the GNMA Mortgage-Backed Securities Dealers Association are located in the city as well as a substantial number of government securities dealers.

ACE Presidnt Nathan Most said in a telephone interview that the new GNMA market is expected to tap pools of funds not yet touched by Chicago traders. "The differences in the ACE contract (compared with the CBOT's) should attract a number of housing and mortgage industry participants that do not hedge in the futures market now," he said.

ACE President Nathan Most said in gage bankers and savings and loan associations to the exchange as well as GNMA dealers and major investment houses, which already participate in such transactions, he said.

"The potential really is incredible," he said. "GNMAs represent just a fraction of the mortgage market but already the m arket has $50 billion contracts outstanding."

ACE also plans to apply next month to trade commodity options on gold and silver bullion under the CFTC's proposed domestic options program. ACE intends to conduct a spot or physical market in those precious metals and will trade options on the physical commodity rather than on metals futures contracts, exchange officials said at the news conference.

ACE's future plans do not include agricultural commodities, such as wheat, corn and soybeans. Most hastened to add.

"We don't see ourselves trading pork bellies," he said. "We believe that agricultural products should be in the Midwest, just as we believe financial instruments should be traded in New York."

"We see tremendous enthusiasm," Levitt added, regarding investor and financial community response to the plans. "I think you are going to see a major development with this new exchange."

The new GNMA contract provides for certificiates to be traded in $100,000 principal balances for delivery in February. May, August and November.Minimum price moves under the the proposed contract would be $31.25 per $100,000. Margins are expected to be about $1,000 a contract.