The Virginia House of Delegates, in a move that surprised the state's influential banking lobbyists, unanimously approved a bill today that would guarantee consumers a grace period to pay credit card bills before they incur finance charges.

Separately, a Senate committee approved legislation that would mandate use of seat belts by Virginia motorists and another Senate committee passed a measure that would force the state's 140 school districts to delay the opening of school until after Labor Day.

Del. Bernard S. Cohen (D-Alexandria), in a floor maneuver that he had kept secret, tacked the credit card amendment onto a related banking bill. Cohen said he expects the Senate to quickly pass the measure, which could come before the chamber Friday. He said it would save consumers more than $36 million a year in interest charges.

Cohen's amendment, approved by voice vote without opposition, would abolish a little-known provision of state law that says consumers forfeit a 25-day interest-free grace period if they carry any outstanding balance from one billing period to the next.

Frowning banking lobbyists watched the televised proceedings from a nearby committee room. Lobbyist Walter Ayers rushed to the floor of the House to assess the damage, saying, "I've got to find out what happened" and refusing to comment further on the bill's impact. Other lobbyists also declined to comment.

Cohen said that about two-thirds of the 2 million credit cards issued in Virginia carry outstanding balances from month to month and that those consumers unknowingly have been paying millions of dollars in extra interest from the date of each charge made. He said the interest in some cases easily exceeds an average of 50 percent or more a year, even though annual credit card rates generally are said to be from 18 to 24 percent in the state.

The bill would affect only credit cards issued by Virginia banks and retail corporations.

Neither Maryland nor the District of Columbia provide the protections of Cohen's amendment, according to a University of Virginia study of credit card billing practices and the Bank Card Holders of America, a D.C.-based consumer group. Maryland's law is the same as Virginia's existing law, and the District provides no grace period on unpaid credit balances.

Cohen was jubilant after the vote.

"I feel like I had a baby," Cohen said as colleagues slapped him on the back and congratulated him.

"The bankers [had] three-martini lunches," laughed House Majority Leader Thomas W. Moss Jr. (D-Norfolk). "After this, they'll have three more."

The Cohen amendment was attached to a bill that would require that banks post payments to customer accounts within two days instead of the five allowed by current law. That portion of the bill already has passed the Senate.

Earlier in the session, Cohen exchanged sharp words with banking lobbyists over his contention that consumers did not understand how easily they could forfeit the interest-free period designed to allow them time to receive credit card bills and pay them.

Banking lobbyists insisted then that most consumers understood how finance charges were computed. A reporter's survey of about a dozen banks in downtown Richmond showed that none of them had any readily available or easily understandable information that explained how interest rates on credit cards are computed.

Cohen said he stumbled onto the law's provision when he allowed a small credit card bill to go unpaid and then was charged interest on a large purchase made later because he had carried over the original charge.

"I think what [Cohen and the House] did today was terrific," said Elgie Holstein, a spokesman for the Bank Card Holders of America. "If it goes through, it will take the hocus-pocus out of the monthly bills consumers get."