THE CLINCH RIVER breeder reactor is the great exception to the Reagan administration's rule against energy subsidies. The White House has never subjected the breeder to the same standards that it has applied elsewhere. Another attempt to rescue the breeder is now taking shape, and once again it requires an exemption to all the Reagan strictures against public spending and lending.

Congress refused any appropriation this year for Clinch River, declaring that there will be no more federal money until and unless somebody comes up with an acceptable plan for a larger share of private money. Part of the electric power industry has now come up with a proposal. The private money would be mainly in the form of loans guaranteed by the federal government. But guaranteed loans are not everybody's idea of a private contribution.

To complete the breeder reactor would, according to the Energy Department, take a further six years and $2.4 billion. The current financing plan comes from the Breeder Reactor Corp., which represents a group of utilities supporting the Clinch River project. This plan proposes that the utilities contribute another $150 million in equity, and the government put up $1.5 billion. The remainder would be raised by the guaranteed bonds, to be paid off by the breeder's power sales.

One obvious difficulty is in the utilities' contributions. State regulators are not visibly enthusiastic about allowing the utilities to pass them on to customers in their power rates.

As for the bonds, Sen. Gordon Humphrey points out that the arithmetic of repayments depends on some cost estimates that seem low and a predicted price for breeder power sales that looks remarkably high. The idea of the bonds arrives in a season when there seems to be rising concern both in Congress and in the administration over the scale of federal lending, and over the use of loans to circumvent the restrictions of a tight budget. It's a bad practice. Why make an exception for Clinch River?

The breeder reactor has only one justification. It gets more energy out of a uranium atom, by recycling it, than the present commercial reactors do. The Clinch River breeder was conceived at a time when it looked as though a uranium shortage lay ahead. But with new uranium discoveries, the economic case for the Clinch River breeder has evaporated at just about the same rate at which the construction cost estimates have been rising.

The immediate question is whether the White House will support this current financing plan with its $1.5 billion appropriation and its bond guarantees. If it applies the same standards to the Clinch River breeder that it applies to all the other energy technologies, the question will answer itself.