Each month for the last 56 months, the federal government has spent an average of more than $13.5 million buying machinery for an electric power plant that may never be built.

The money spent so far on the Clinch River Breeder Reactor totals more than $850 million, most of it for valves, pumps, water tanks, steam generators, heat exchangers and a massive stainless steel reactor vessel that stands over five stories high and weighs more than 500 tons. Like most of the rest of the machinery, the reactor vessel was put into a warehouse three months ago where it may stay for years to come.

The White House and the Congress have been locked in combat over Clinch River since 1977, when President Carter ordered that it not be built because it would breed plutonium and plutonium is a danger to world peace. Carter though differently and has appropriated enough money in the last three years to fill three warehouses in the country with machinery for Clinch River.

The House subcommittee on energy research, chaired by Mike McCormack (D-Wash.), yesterday approved a Clinch River budget for for fiscal 1981 of $155 million, which is $17 million less than it authorized for fiscal 1980. Still it is $155 million more than the Carter administration asked for this year, the year before or the year before that.

What $155 million will buy is another year of time, as well as some of the few remaining components that will be put into the plant if it ever gets built. It also keeps a lot of engineers at their drawing boards designing the final plans for Clinch River.

"As long as President Carter persists in this obstructionism, Congress can do nothing but appropriate the money to buy the components for Clinch River," McCormack said. "Even if we started now to build Clinch River, we're nine years behind our original schedule and 16 years behind the rest of the world."

How did the nation manage to reach such an expensive standoff on Clinch River? To hear people on each side tell it, the Carter administration made a serious mistake when it set out in 1977 to kill the project on grounds that Clinch River would encourage other countries to build breeders, produce plutonium and make atomic weapons.

"The original arguments were too strident," conceded John M. Deutch, undersecretary of energy, who will resign next month to go back to teaching chemistry at Massachusetts Institute of Technology. "I don't think the neoproliferation argument ws an appropriate one for the cancellation of Clinch River."

What would have been appropriate, Deutch said in an interview, would have been to cancel Clinch River because its design was out-dated, its technology obsolete and its construction premature.

"I think the Congress had an early commitment to the technology [and] they may have been a little resistant to the economic arguments that say we don't need a breeder yet," Deutch said. "But now there is a waste of about $16 million a month that I don't think we can afford on our technology bill. I think it's a catastrophe for the country not to resolve this."

McCormack says he met privately at the White House a year ago with President Carter in an attempt to reach a compromise. McCormack said he told the president he would commit Congress to an agreement that would end Clinch River if the president would commit the country to a new breeder project.

"The president rejected the compromise," McCormack said. "He gave it no consideration whatever. Since then, the Congress has had no option but to go ahead with the Clinch River project."

And so it goes. The White House refuses to commit the United States to a new breeder. Congress goes right on appropriating money for the old breeder and barges carry the finished machinery to a pair of warehouses in Memphis and Oak Ridge, Tenn., that cost more than $1 million a year just to maintain. The massive rector vessel that was finished in December is the only Clinch River component not stored in the two Tennessee warehouses. To save transportation charges, it was put in storage at Mt. Vernon, Ind., where it was built.