American Express Co. and the big brokerage house of Bache Halsey Stuart Shields Inc. announced today that the two companies would cooperate in a joint venture in which account holders at Bache could tap their funds using a special American Express Gold Card.

The new account, which will not be available until at least the first quarter of 1982, will be similar to the highly popular Cash Management Account (CMAs) pioneered in 1977 by Merrill Lynch, Pierce, Fenner & Smith Inc. That account allows Merrill Lynch customers to have their excess funds and have access to those excess funds through a checking account and a Visa debit card.

The special American Express Gold Card that Bache customers will receive will also be a debit card, which means that funds will be deducted immediately from their accounts when a Gold Card receipt is presented for payment.

In the sometimes strange happenings on Wall Street, American Express is in the process of acquiring one of Bache's competitors, Shearson Loeb Rhoads Inc. Bache's parent company, The Bache Group Inc., is being acquired by Prudential Insurance Co., the nation's biggest insurer.

A spokesman for American Express said the financial services giant has talked to several major brokers about coupling the Gold Card with CMA-type account. "Our acquisition of Shearson did not change that strategy," the spokesman said. Shearson is rumored to be its own CMA-type account that presumably also would be linked to an American Express Gold Card.

Investor interest in the Merrill Lynch Cash Management Accounts has been growing sharply in recent months. About 300,000 investors now have the so-called CMAs, with more than 100,000 signing up in the last few months. The accounts give financial flexibility and high-interest returns to funds that normally sat in what are called margin accounts at brokers.

Other brokerage firms were slow to respond to the Merrill Lynch move but have become aware that they are losing customers to Merrill, by far the country's largest broker.

"They were first with a good product," said Jim Settel, senior vice president of Bache. "Ours will have to be better." But Settel would provide few specifics on Bache's proposed account, saying that many details yet have to be worked out.

Dean Witter Reynolds is ready to introduce its own CMA-type account and other brokers, such as Shearson, are thought to be ready to announce their own special margin accounts.

The normal American Express Gold Card is issued in conjunction with a bank, and the cardholder has a line of credit with the issuing bank. The special card issued with the Bache account will not have a bank line of credit.