A special State Senate subcommittee ruled today that senators who own bank stock, serve on bank boards or represent banks in their private law practices can vote on banking bills.

Two hours later, another Senate committee voted 7 to 2 to abolish the state's 18 percent ceiling on interest rates that banks charge to credit-card customers with unpaid balances. Five of the seven senators who voted for the measure list private banking interests on their Senate financial disclosure forms.

The subcommittee's ruling had been requested by the chairman of the Senate Banking Committee, who warned that recent controversies over alleged conflicts of interest against Sens. Nathan H. Miller (R-Rockingham) and Willard J. Moody (D-Portsmouth) had so frightened senators that his committee would not be able to muster a quorum on the credit card bill.

"Ever since Moody and Miller got raked over the coals, everybody has been gun-shy, including me," said chairman William E. Fears (D-Accomack), who later voted for the credit-card measure. "I own bank stock. I didn't know whether I should vote on this thing or not."

The bill, promoted vigorously by the state's banking industry, already had passed the House of Delegates by a wide margin. If it wins the approval of the Senate, banks are expected to respond by raising interest rates on revolving credit card accounts to 19 or 20 percent.

According to the subcommittee's report, a senator need not refrain from voting on the interest bill unless he or she has an immediate, private or personal interest in the legislation. That interest might be proven, the report said, if the senator receives at least $5,000 annually from the bank, or has a 5 percent ownership interest in the bank, or if the senator's bank had requested the legislation, or was one of the few banks issuing credit cards.

Three of the five subcommittee members who helped draw the report, including Sen. Adelard L. Brault (D-Fairfax), also listed some financial interest in the banking industry on their Senate records.

Virginia senate disclosure rules are considered among the nation's weakest, and do not require legislators to disclose how much stock they hold in banks, how much income they receive from them, or even the names of the banks in which they have an economic interest.

Among those voting in favor of the interest rate measure today were Sen. Elmon T. Gray (D-Sussex), a director of First and Merchants National Bank and chairman of the board of the Bank of Waverly; Sens. Peter K. Babalas (D-Norfolk) and Clive L. DuVal (D-Fairfax), who list several unnamed banks on their senate disclosure forms; Sen. Elliot S. Schewel (D-Lynchburg), a director of Virginia National Bankshares, and Fears, who lists "local bank stock."

Abstaining on the measure were Miller, who lists himself as a stockholder in Rockingham Savings and Loan Association, and Sen. Frederick C. Boucher (D-Abingdon), a member of the board of directors of the Bank of Damascus. Sen. Edward M. Holland (D-Arlington), a director of First Virginia Banks, failed to vote on the measure, as did Moody, a director of the Bank of Virginia.