"Why not the best?" Jimmy Carter kept asking in the presidential campaign as if there were no conceivable answer. But there is an answer so traditional as to qualify as folklore.

The answer is that "the best is the enemy of the good." The painful rediscovery of that ancient truth summarizes most of what has happened in the first year of the Carter administration.

Honest government represent the area where Carter most effectively articulated his dedication to high standards. As a candidate, his position as an outsider combined with plain style, religious idiom and constant assertion of righteousness to give bright promise of departure from those shoddy ways so widely prevalent in Washington and other power centers.

As President he has lived up to the promise to a considerable degree. The insolence of office that characterized the Nixon administration has been importantly reduced by Carter and his men. The integrity of most of those appointed, and their keen desire to do good - their moral ambition, so to speak - cannot be seriously doubted.

But one grivous exception to the maintenance of the highest moral standards - the case of Carter's friend and former budget director, Bert Lance - has made some of the President's moral promises look hollow. Moreover, he has been obliged to compromise with established forces in virtually every other area.

Most notably this has been true in his dealings with the Congress. Carter started off by standing fast against a cherished bit of congressional patronage: water projects. He thus inadvertently forged an anti-administration coalition of Republicans and Democrats representing producer states. That alliance has come to dominate the Senate, where it held up two pieces of business on which the Carter administration staked its reputation: approval of the Panama Canal treaties and the energy bill.

To get those measures through this year, Carter has had to deliver himself bound the practically gagged to two senators notorious for their accommodations with established interests: Majority Leader Robert Byrd and Russell Long, chairman of the Finance Committee. It is an open question whether Sen. Long's greedy demands on energy won't in the end produce a bill that undermines the authority of Carter's most important congressional asset: Tip O'Neill, the Speaker of the House.

The reversion to type in relations between the White House and the Hill has characterized all other features of the Carter administration. His most important new departure in foreign policy centered on an effort to achieve a comprehensive settlement in the Middle East by bringing all parties together at a Geneva conference. That prospect so worried the Egyptians and Israelis that they took matters into their own hands, initiating a process highly reminiscent of Henry Kissinger's "step-by-step diplomacy."

In dealing with the Russians, the President went for the brass ring: progress on human rights and deep cuts in the levels of strategic weapons. He so alienated the Russians that he missed the deadline for a second-stage agreement on arms control. To get such an agreement he has soft-pedaled the human-rights issue and is working on an arms-control accord based on the 1974 outlined developed by President Ford at Vladivostok.

None of the other foreign-policy innovations - emphasis on Africa and stopping nuclear proliferation and non-interference in allied countries - has panned out any better. Indeed, Carter wound up his first year selling nuclear plants to Iran, going nowhere in Africa and warning against the threat of communism in Italy.

In domestic affairs Carter started off with brave plans to stimuate the economy and fight inflation by direct restraints on prices and wages while reforming abuses in the tax and welfare systems. He has been obliged to push reform onto a distant date. He has virtually abandoned any hope of direct curbs on prices and wages.

Agriculture and other interests have stuck him with a series of highly inflationary measures. His plan for stimulating the economy rests largely on tax cuts designed to build business confidence, which he lost by having to renege on his initial plans.

Despite the administration's almost systematic retreats, however, nothing very bad has happened either at home or abroad. So at his juncture probably the most important thing to be said is that the country has not had to pay a heavy price for the education that made up the first year of the Carter administration.