At 2 a.m. on a crisp June morning, the muffled roar of bulldozers and the chatter of pneumatic drills reverberate across the sleepy wooded valley of the Clinch River.

Under the glare of incandescent lights, the late shift is working far into the night excavating rock from a huge hole being dug for the foundation of the Clinch River breeder reactor.

In Washington, congressional foes of this advanced atomic power plant--called a breeder because it will "breed" more plutonium fuel than it consumes--think they finally have the clout to kill the nation's most controversial civilian nuclear project.

But 13 years after it was born--and six years after President Carter began trying to choke off its development and construction--the Clinch River breeder, like some sci-fi nuclear mutant, has become the reactor that refuses to die.

"We keep killing it on the House side, and then it keeps coming back," complained Rep. Judd Gregg (R-N.H.), a critic of the project, during a recent debate.

Despite the many brushes with death that the Clinch River breeder has survived in recent years, its judgment day finally may be close at hand.

The House three weeks ago, on a vote of 388 to 1, approved an amendment to an authorization bill banning further federal spending on Clinch River as of Sept. 30 unless an acceptable plan is devised to shift more of the remaining cost--at least $2 billion--to private utilities.

While it remains uncertain whether the Senate will go along with the funding cutoff, the announcement by Senate Majority Leader Howard H. Baker Jr. (R-Tenn.)--who barely rescued his home-state project last winter--that he will retire at the end of this term may make it harder for him to save the breeder one more time.

Nevertheless, the amazing ability of the Clinch River breeder to survive in and adapt to a hostile environment can be seen in the construction taking place here.

Despite the impressive array of 70 large earth movers, bulldozers, cranes, and rock haulers rumbling about this 220-acre site, kicking up a cloud of dust as the red clay dries out from spring rains, work here never officially is called "construction." Instead it is called "site preparation."

The reason for this semantic charade is that Congress last winter, as part of the compromise that kept the Clinch River breeder alive, banned "construction of any permanent facility structures" at the site until the future of the project could be debated and put to a vote.

This was interpreted to mean that the Reagan administration, which unlike its predecessor strongly favors the project, could clear the brush and southern pine from this knoll that juts out into the Clinch River and even start work on excavation, but it could not pour concrete.

From the project management's standpoint, that was acceptable since it does not have a full construction permit yet from the Nuclear Regulatory Commission, and even with workers going all out, the huge hole being dug for the foundation could not be completed until fall anyway.

What's more, the breeder's backers believe that each month the project is kept alive--with more gleaming components arriving to be stored in warehouses, and work at the site now under way--the odds increase that the Clinch River reactor someday will fission to life.

"We are not having the snoot-under-the-tent approach," Chairman Don Fuqua (D-Fla.) of the House Science and Technology Committee recently assured opponents of Clinch River who expressed concern over the $16 million now being spent on site preparation.

In fact, not only the camel's nose but much of the hump long since has been in the tent, with $1.5 billion spent on the project over the past decade, and 75 percent of the major components either on order or already delivered.

"We're getting to the point where all we have to do is put the pieces of this erector set together," said Percy Brewington Jr., the acting project director.

Given the polarization of the national debate in the United States over nuclear power, it hardly seems surprising that its supporters and opponents have made the breeder--symbol of the atomic frontier--the focus of the most vehement debate.

Starting with Carter, who sought to delay development of this advanced reactor out of concern that foreign countries would use its ability to "breed" plutonium as a way to build nuclear weapons, critics have attacked Clinch River on a shifting variety of energy, economic and emotional grounds.

Even supporters of breeder development, in a country where consumption of electricity declined last year, no longer echo the arguments of the 1970s that large numbers of breeder reactors will be needed to meet America's energy requirements early in the 21st Century.

"But it's dumb to forget why we are doing this," said Alvin Weinberg, director of the Institute for Energy Analysis at Oak Ridge Associated Universities. "If you say you are building the Clinch River breeder to demonstrate an economical device, then you are kidding yourself unmercifully.

"But this country since President Truman has made a commitment to the notion that it is the national purpose to develop inexhaustible energy resources. The breeder is one of three, along with solar and fusion.

"When will we need the breeder? Gosh, it might be 50 or 75 years," Weinberg conceded. "But look at the difficulties we have in nuclear energy today. Many old-timers in the field would say it is because we went too fast.

"My argument for Clinch River is, since you have put over $1 billion into the thing already, go ahead and build it, and there are many things you will learn during its operation."

The criticism that most infuriates the team working to build Clinch River is the suggestion that because this breeder was launched in 1970, it must be outmoded, a "technological turkey."

Officials counter that when the project, which originally was targeted for completion in 1980, was slowed by Carter, they took advantage of the delay to redesign and update many of the systems.

"The critics call it names--technological turkey, white elephant, vampire--but they really don't have anything behind the names to tell you what is obsolete," said William F. Rolf, general manager of the consortium of 753 utilities that have pledged $257 million to the project.

"A substantial number of technological innovations have been cranked into Clinch River during this national policy debate," added Charles H. Fox Jr., assistant director for engineering. "We have the most sophisticated core design in the world. Our components are on a par with anyone else. As of right now, we are not behind the state of the art."

"If we started today from scratch to build an intermediate breeder, it wouldn't look exactly like this one," conceded Gordon L. Chipman, deputy assistant secretary of energy for breeder reactors. "Every project that is ever built, by the time it is built, if you started it over would look somewhat different.

"But the point on Clinch River is the technology has been kept up to date. We have moved ahead trying to keep everything as modern and advanced as we possibly could," said Chipman.

Officials of Westinghouse, who have built a mockup of the Clinch River control room in a building near the site, also have made "major improvements" in its design on the basis of lessons learned from the 1979 accident at Three Mile Island in Pennsylvania.

"We have provided for a maximum of reliability for the safety controls and communications. We have made the basic safety functions automatic, and that is state of the art," said Pete Planchon, manager of plant systems. "It is significantly different than you would find in any of today's light-water reactors."

Out at the site, meanwhile, workers have dug 100 feet through the clay and limestone, and now are drilling and blasting their way through the siltstone, on which the reactor will be based.

"We've moved a little over 1 million yards of dirt to date and about 500,000 yards of rock," said Richard A. Chidlaw, assistant director for construction. "We've got about about another 40 feet down to go."