Amid warnings about sounding a death knell for nuclear power in the United States, the Senate Energy Committee yesterday voted - again - to let the Carter administration kill the controversial Clinch River breeder reactor.

By a vote of 11 to 8, the committee agreed, as it had done two weeks ago, to the termination of the Tennessee fast breeder reactor project, so long as the administration gets to work promptly on the "conceptual design" of another, possibly safer, nuclear power plant.

The action, concluding what Sen. John Melcher (D-Mont.) called a "weird dance" around the issue, came as the committee approved a $10.4 billion authorization for the Energy Department's civilian activities. With it went a formal request for absolution of the committee's tardiness; all authorization bills were supposed to have been cleared for Senate floor action by May 15.

The Clinch River issue had ostensibly been settled within the committee June 8, when it reluctantly adopted a proposal by Melcher for a new fast-reactor design which "shall use" a proliferation-resistant fuel cycle. One of the principal objections to the Clinch River project was the amount of plutonium suitable for nuclear weapons that it would keep breeding to fuel itself.

Assigned to reduce the senators' decision to legislative language, the committee staff inexplicably ignored Melcher's mandatory tone and instead decreed that the Department of Energy should "consider" a proliferation-resistant fuel cycle in its new design.

Melcher noticed the discrepancy last week and the wrangling began all over again.

Yesterday the Montana Democrat proposed also to make clear that no new construction could begin without congressional approval of the substitute design. This encountered a fresh barrage of rhetorical resistance, but in the end, the objectors voted for the Melcher proposal, apparently taking comfort in the fact that it requires Energy Secretary James Schlesinger to come up with a new design by March 31, 1981.

Sen. James McClure (R-Idaho), an-protested that the committee was doing little more than authorizing a vague study that would result in "a lot of wasted money." He said he would prefer to bury the Clinch River project without further pretense.

"We're killing nuclear energy in this country," Johnston warned. He said that at a White House meeting last week, utility industry executives bluntly told President Carter they were not going to build any more nuclear plants unless the administration went ahead with the breeder reactor.

Sen. James McClure (R-Idaho), another supporter of the Clinch River project, protested that at the same meeting Carter said: "We don't need it, at least not now - not until the year 2020."

Even worse, McClure said, Schelesinger stated that "We can always find fuel overseas . . . and if we need a breeder, we can always buy it from the French."

"That kind of reasoning . . . is a disaster for this country," McClure declared. "I don't think we can afford to build a nuclear dependency in this country in the same way we depend on foreign supplies of oil."

Despite the rhetoric, both Johnston and McClure ended up voting with the majority to require congressional approval of any new "conceptual design" that DOE proposes. Dissenters included critics of the Clinch River project such as Dale Bumpers (D-Ark.) and John A. Durkin (D-N.H.), who argued that Congress had no business approving a complicated nuclear project design.

"They could send up the design for a deregulated gas station" and Congress wouldn't know the difference, Durkin suggested.

The issue will come up again in conference with the House, which has tentatively voted to continue Clinch River.

The Senate committee also approved, almost without discussion, $119 million for projects that Sen. Frank Church (D-Idaho) had described as needed for the "liquid metal breeder reactor basis program," including $30 million for a safety research experimental facility at the Idaho national engineering laboratory.

Melcher told a reporter after the session that he deemed all this "confusing and unnecessary," but felt it was still clear that all sorts of "proliferation-resistant" technologies, such as gas-cooled fast reactors, should be explored.