In its first legislative response to allegations of Chinese spying, the Senate voted overwhelmingly yesterday to give responsibility for nuclear weapons research and production to a new agency inside the Department of Energy.

The 96 to 1 vote reflected strong sentiment in Congress that security must be tightened at nuclear weapons laboratories. But it is uncertain whether the House of Representatives will agree that a semiautonomous agency is the best way to achieve that aim.

If the Senate plan eventually is adopted, it will mark the first major reorganization of the nuclear weapons complex since the Energy Department was created. It also would be the most significant change yet produced by a report on Chinese espionage issued this year by a bipartisan panel headed by Rep. Christopher Cox (R-Calif.).

The new agency would control the Los Alamos, Lawrence Livermore and Sandia national laboratories as well as the Nevada nuclear test site; production and assembly plants in Texas and Missouri; nuclear materials facilities at Oak Ridge, Tenn., and Savannah River, S.C.; the U.S. Navy reactor program; and the Energy Department's international programs to combat proliferation of nuclear weapons.

The Senate passed the plan as an amendment to a bill authorizing the fiscal 2000 budget for U.S. intelligence operations. The amount of the intelligence budget is classified but is usually estimated at $27 billion.

Sen. Ron Wyden (D-Ore.), who cast the sole vote in opposition, said he opposed the bill because it could permit the new agency to reopen a nuclear reactor in his state without adequate environmental precautions.

The proposed Agency for Nuclear Stewardship would be run by a new undersecretary of energy. Energy Secretary Bill Richardson would establish overall policies for the agency and supervise the undersecretary, but other top Energy Department officials would not be able to direct the agency's operations unless they acted through Richardson or his deputy.

Richardson initially opposed the new agency as a "fiefdom within a fiefdom" and contended that he had already taken adequate steps to bolster security by naming a new counterintelligence chief and a "security czar." In recent weeks, however, he said he would accept the plan as long as it did not diminish his authority as secretary.

The plan was proposed in May by three Republicans, Sens. Jon Kyl (R-Ariz.), Pete V. Domenici (R-N.M.) and Frank H. Murkowski (R-Alaska). Kyl said yesterday that "this is a first major step in preventing the future theft of our secrets, but there is more to do."

Senate Democrats went along with the plan after amendments were adopted to clarify that Richardson would retain "direction, control and authority" over nuclear weapons policy, including counterintelligence and security at the national labs.

Some members of the House, however, favor creating a fully independent agency that would not report to Richardson. Others want to leave the Energy Department in control of the nuclear weapons complex but change the organizations -- including the University of California -- that run the labs under contract.

Rep. William M. "Mac" Thornberry (R-Tex.), whose district contains the Pantex nuclear weapons plant, predicted yesterday that the House eventually would go along with the Senate plan. But Rep. Ron Klink (D-Pa.) argued this week at a subcommittee hearing on security that creating a new agency "would very possibly make the accountability situation worse than it is now." The Senate plan, he added, would give the national laboratories "more independence and lack of oversight than ever before."