A Virginia legislative subcommittee today effectively killed legislation to allow the state's public schools to adopt a four-day week as a way of conserving energy resources.

Worried that four long school days would leave children mentally fatigued, a Senate education subcommittee recommended instead that the State Board of Education conduct a one-year study of the plan's potential impact on students and energy supplies.

"Our concern is the welfare of the children," said Sen. Edward E. Willey (D-Richmond), a member of the subcommittee and one of the Senate's most influential leaders."There's just so much a child and take and you can't put too much of a burden on them."

Although the subcommittee's vote could be reversed by the full education committee, several legislators said they believed that it was extremely unlikely with the four-day week bill.

The proposal, introduced by Sen. William E. Fears (D-Accomack) would have allowed school officials to adopt a four-day week provided that such a schedule offered as much instructional time as the five-day schedule does.

Currently, Virginia public schools are required to offer 180 days of instruction, at a minimum of 5 1/2 hours of instructional time a day. If four-day weeks were instituted, legislators estimated, students would need to attend school for six hours and 52 minutes each day.

Fears stressed that his measure was not a mandate for four-day school weeks, but an attempt to give local school officials an emergency option when cold weather and high energy costs squeeze their budgets. He estimated that passage of the bill would permit school districts to save up to 25 percent on the cost of fuel for school buses.

Testimony from state school Superintendent S. John Davis, however, cast doubt on Fears' statements. Davis told subcommittee members that an abbreviated school schedule would not necessarily result in big energy savings because many schools are kept open for such community functions as church services.