A PRESIDENT'S FIRST VETO is more than a statistic. It is a political rite of passage. The second, third and fourth vetoes, and on to infinity, are not "events" in the same sense. Since most Presidents, especially those dealing with Congresses of their own party, do not like to admit the "failure" of needing to veto legislation, there is a more-in-sorrow element to the first veto - and a corollary assumption that only a matter of considerable importance to a President could have provoked so unhappy an act. Saturday Jimmy Carter chose to bestow this honor on legislation demanding him to go forward with the Clinch River breeder reactor demonstration plant. He could not have chosen a more fitting object, in our view. The Clinch River legislation richly deserved to be blocked, and it also raised sufficiently important policy questions to have induced Mr. Carter's first veto - an action the President had evidently hoped to avoid taking at all this year.

The legislation in question would have compelled the administration to go ahead with what President Carter rightly called "a large and unnecessarily expensive project which, when completed, would be technically obsolete and economically unsound." To do so, as he observed, would be to divert effort from preferable energy projects (including a better-paced and more promising breeder reactor program) and to squander enormous sums of taxpayers' money ("Its total cost estimate now exceeds $2.2 billion").

The waste at home would be matched by risk abroad: a damaging, go-ahead signal to those countries Mr. Carter is trying to persuade to defer pursuit of the dangerous plutonium techonolgy so that less bomb-prone alternative nuclear-energy sources can be explored.It is far from certain that the President will have any luck in his anti-proliferation diplomacy. But the chances would hardly be improved by American pursuit of a plutonium-breeding facility already widely regarded as a technological turkey.

Mr. Carter had other and more detailed objections to the legislation, from its attempt to limit his constitutional authority by means of some one-House veto provisions to its implications for his plans for dealing with spent nuclear fuels. But his two larger objections are the key ones: the wasting of precious resources at home and the inhibition of his efforts to limit the spread of nuclear weapons abroad. There are some very dicey political maneuvers yet to come, and the outcome of the President's action is anything but certain. Congresses have been known to view a President's first veto as something that must be over-ridden to put him in his place. The industry lobbying on this project has been super-intense. And Congress could always raise the ante by attaching the terms of the legislation in some form to other measures. Reportedly, Mr. Carter knew all this when he decided to veto this authorization. He had announced his intention earlier in year to defer the Clinch River project and he meant to stay as good as his word.

Because being overriden or otherwise stared down on a first veto has ripple effects of damage to a President that go beyond the subject at hand, Mr. Carter was taking a pretty hefty risk in deciding to cast his first veto on this bill. It was, in our opinion, worth the high risk, and will be worth a fight of whatever severity is required to see it through. We think the President has shown good judgement on this one, sound values and, yes, political courage.