Visa U.S.A. has agreed to pay $7 million in cash and notes to four regional financial institutions for Maryland Switch Inc., a Baltimore-based electronic funds transfer system, and Service Center Inc., a payment card and travelers check processor, the bank card company announced yesterday.

The purchase is a critical step in establishing a strong response in the banking industry to non-bank competitors' advances in electronic funds delivery systems, Visa U.S.A. officials said in telephone interviews yesterday.

Although Visa U.S.A. and directors of Maryland Switch have agreed to the terms of the purchase agreement, the transaction probably won't become effective for at least six weeks, a Visa official said.

Maryland Switch is a regional automatic teller machine and point-of-sale interchange, or computer switching network, which began operating in 1976. It is owned by Suburban Bank of Bethesda, First National Bank of Maryland, the Savings Bank of Baltimore and First Virginia Bank in Falls Church. It is the switching system for Network Exchange, a regional ATM network linking machines owned by a consortium of financial institutions in the District, Maryland and Virginia.

Service Center Inc. is owned by Suburban, First National Bank of Maryland and Equitable Bank of Baltimore.

Visa plans to operate Maryland Switch as a subsidiary and "to keep everything as is" because "present management is quite strong," said David A. Huemer, executive vice president of the San Francisco-based company.