The Commodity Futures Trading Commission opened the way for a broad expansion of futures based on interest rates yesterday by approving four proposals for futures trading in government securities.

The CFTC approved two plans for futures contracts on 90-day Treasury bills and two plans for a future contract based on four- and six-year Treasury notes.

The new contracts are meant to allow investors who think interest rates will go up or down to buy or sell futures contracts and profit by the changes in interest rates.

A speculator who believes short-term interest rates are going up could buy a 90-day T-bill futures contract that would become more valuable if rates do rise.

Trading in the new contracts was approved unanimously yesterday by the CFTC after months of delay and extensive negotiations with the Federal Reserve Board and Treasury Department, which initially raised major objections to the contracts.

CFTC Chairman James M. Stone said that if there is any indication the futures trading is interferring with the Fed and Treasury's management of government financing, he'd reconsider the new contracts.

Commissioner Read P. Dunn, who handled the lengthy study of the new contracts, said the action "is almost like going into a complete new era of future trading."

Traditionally futures markets have dealt in contracts for ruture delivery of commodities like wheat or corn. Flour millers fearing wheat prices would rise could buy wheat futures to protect themselves against the price increase while speculators, hoping the price would fall, would sell contracts to deliver wheat later.

The contracts approved yesterday will allow trading in 90-day Treasury bill futures on the Amex Commodity Exchange (an offshoot of the American Stock Exchange) and on the Commodity Exchange Inc. also in New York. The two contracts would be similiar, but for T-bills maturing in different months.

Also approved was a Chicago Board of Trade futures contract in four to six year Treasury notes and a Chicago Mercantile Exchange Contract in four-year Treasury notes.

The Chicago Board of Trade said it hoped to have its T-note pit open by next Monday and the Amex said it was preparing to begin T-bill futures trading next Tuesday. The other exchanges are expected to launch their new markets as quickly as possible.

The CFTC since last fall has allowed experimental trading in some government securities futures, bu tyesterday's action is expected to broaden the trading considerably.

Commodity industry officials say they expect the new markets to attract speculators who believe they can out-guess the market on the direction interest rates are going and hedgers who want to protect themselves against changes in interest rates by making futures market commitments.