Merrill Lynch, Pierce, Fener & Smith, Inc., today announced a comprehensive new brokerage account for customers that will give the country's largest securities firm a toehold in banking and move it closer to its goal of becoming an all-purpose financial department store.

Merrill Lynch chairman Donald T. Regan said the program was "in effect the first step in a nationwide electronic funds transfer system."

Called the "cash management account," it will let customers earn interest on cash balances held with Merrill Lynch. Brokers currently do not pay interest on uninvested funds they hold.Merrill Lynch will put these funds into one of its so-called "money market" mutual funds.

Customers, through use of a specially issued Visa (formerly BankAmericard credit card and special bank checks, will in addition get nationwide, immediate access to these funds and also to loans from Merrill Lynch up to the margin value of securities held with the firm.

The loans, collateralized by the secutities, will be offered at Merrill Lynch's regular margin account rates, currently between 6.5 per cent and 8 per cent, depending on the size of the loan. These are generally much lower than the rates on consumer loans obtainable directly form banks.

Scheduled to begin this September, the "cash management accounts" will initially be limited to customers in Atlanta. Denver and Columbus, Ohio. If the pilot program proves successful, Merrill Lynch will extend it throughtout the country, Regan said, 'a's quickly as possible."

Merrill Lynch has not yet decided what it will charge for the new account, Regan said, but it will probably be between $2 and $5 a month. To qualify, a customer must be eligible for a margin account, which requires a minimum of $2,000 in security or cash. The program is being offered in conjunction with City National Bank of Columbus, Ohio, a $750 million institution, which will provide check and credit card processing, immediate debeting against accounts and record keeping services to Merrill Lynch customers. The bank is the country's second largest processor in the Visa card system. The Bank of America is the first.

Merrill Lynch will provide to customers a monthly statement summarizing all transactions, including purchase and sale of securities, dividends received or interest due, drafts and credit card purchases.

Regan said he did not foresee any regulatory difficulties. He said he had been advised by lawyers that the program does not require any specific regulatory approval.

Most brokerage firms declined to make any immediate comment on the Merrill Lynch proposal and their own plans.

"We're looking at a number of things along those lines but have nothing definite as yet," a spokesman for Paine, Weber, Jackson & Curtis said.

The "cash management account," according to an example offered by Regan, would work this way. A customer with $20,000 in securities held by Merrill Lynch will have available to him $10,000 in a credit line based on his margin account, or 50 per cent of his holdings.

Suppose with liquidation of some securities and dividend payments he accumulates $1,000 in cash. This will be deposited in a money market fund where dividends are earned daily, based on prevailing short-term rates. Merrill Lynch will charge its normal fee of 1/2 of one per cent of funds under management as its annual fee. New deposits will be made weekly.

If the customer wants to buy an automobile costing $5,000, he can use his Visa card or a bank draft to pay for it, with $1,000 withdrawn from his money market fund shares, and the remaining $4,000 in the form of a loan based on his margin account credit line. The cost of the loan, based on current interest rates, would be 8 per cent. (The cost of the loan goes down as the size of the borrowing goes up, with a 6.5 per cent applied to borrowings over $50,000.)

A customer with the new account could use his Visa card at any of the 50,000 worldwide branches of the 8,700 banks in the Visa/BankAmericard system, as well as at all establishments accepting the card. The payments would automically be made either by releasing balances invested in money market fund shares or by drawing down the available credit line.