With Congress finally and blessedly gone for a month, Year Five of the Reagan administration is just about over. It has been short of specific accomplishments -- but still a year of large-scale and long- term significance.

When I wrote recently that Republican governors were trying "to move the Reagan revolution beyond the Washington beltway," a reader objected that "there has been no Reagan revolution inside the beltway since 1981." Ever since the original sweeping defense, budget and tax bills were passed that first summer, he said, President Reagan has been mired in the usual Washington glue.

I disagree with that thesis, but it is certainly true that 1985 was not the year it might have been. Reagan's issue-free, feel-good 1984 campaign created no policy mandate. For much of this year, the newly reelected president was on the defensive.

Early in the year, Reagan was forced to fend off nearly successful challenges from Capitol Hill to his MX missile program and his aid to the contras in Nicaragua. Later, he and his new chief of staff, Donald T. Regan, underestimated the political forces propelling such diverse causes as farm and trade relief, sanctions on South Africa and a curb on wasteful defense procurement. On each of these issues, he was forced into improvised, catch-up actions.

He poured much of his energy into selling a tax-revision program that never developed a mass public constituency. It divided him from his most loyal lieutenants in Congress, was barely alive at the end of the year and still faces its highest hurdles in the Senate.

He failed, once again, to devise a budget plan plausible enough to command support from either party in Congress. Instead, with another $236 billion added to the debt this year, he acquiesced reluctantly in a congressional deficit-reduction process that his principal defense and foreign policy advisers consider a threat to national security.

The signal moment of the year, the summit conference with Mikhail Gorbachev, was a public-relations triumph. But the summit failed to close the gap between the superpowers on arms control, human rights, regional conflicts or anything else more substantive than cultural exchanges. It did not even resolve the internal debates within the administration on the best way to approach the Russians on nuclear issues.

In the face of that record, why do I still talk about "the Reagan revolution" or assert that this has been a year of "large-scale and long-term significance"? Because Reagan is a practitioner of what I have come to think of as Archimedes' politics, of leveraged change based on the dictum, "Give me where to stand and I will move the Earth."

Reagan stands historically high with the American people -- and for good reason. The economy has gone through its third year of healthy, non-inflationary growth. International tensions have eased. Whatever his shortcomings as chief of government, they are publicly overshadowed by the grace with which he functions as chief of state in moments of national tragedy and triumph.

Reagan's strength increasingly translates into strength for the Republican Party and that, in turn, increases his leverage. Republicans have now maintained near-parity with Democrats in voter identification for more than a year -- unprecedented in the past half-century. They have a decent chance to hold the Senate in 1986 and a better chance to increase their share of governorships, which would break the "six-year jinx" that regularly afflicts the party in power. With that kind of 1986, Republicans may be just one election away from the elusive goal of long-term political realignment.

Beyond these durable personal and partisan gains, Reagan has engineered a set of policy changes that do constitute a long-term revolution in government.

By his continued downward pressure on non- military spending and on tax rates, he has shifted the initiative in domestic policy out of Washington and into the states, achieving a cherished conservative goal. That shift will continue and accelerate under the Gramm-Rudman budget process and the House-passed tax bill.

By his continued advocacy of military increases and the Strategic Defense Initiative, he has forced the Soviet Union to reconsider its own military strategy and its relationship with the United States. That reevaluation will continue in the next few years.

By his repositioning of the Justice Department and his restaffing of the federal judiciary, he is forcing a similar large-scale change in social policy. That, too, will continue as more Reagan judges rule on more civil rights, environmental and regulatory issues.

All of these changes are controversial, but all of them proceed from Reagan's sure sense of purpose and his political leverage. He must be measured, not in the specific gains and losses of one year, but by the large-scale, long-term gauge we use for presidents of historic dimension.