In this summer of the '70s, a decade marked by growing national disillusionment with the political process, Jimmy Carter has been give one last chance to save his presidency and restore some of the power and prestige of his office. Failure to seize this opportunity would almost certainly make him the fifth straight president unable to survive in office.

No president has ever been reelected after standing as low in the polls as Carter does today. Few have faced such rapidly deteriorating political conditions. Even fewer have seen events shape a simple moment where a bold presidential stroke can alter the course of affairs.

Critics say Carter already has missed his chance. By suddenly, inexplicably canceling his highly publicized national address on the overriding concern of the country, energy, at a time of rising anger and apprehension over the future, he has reinforced the public impression of his weakness and indecision. But that doesn't have to be the way this extrodinary chapter in his presidency ends.

What Carter is doing, once again in the seclusion of Maryland's Catoctin Mountains, is building a drama of many parts. Whether the fashioning of this drama is accidental of Machiavellian matters not. It now has a life of its own: the longer the silence from the summit, the greater the suspense. The more people consulted in secret, in or out of government, the greater the anticipation. One way or another there will be a final act. Carter's fate will hang upon it.

For some time one of the president's concerns has been how best to reach the public. Amid the increasing national preoccupation with self, with the Me-ism of the times, the turnaway from public affairs and public questions, how does this soft-spoken, instinctively un-demagogic president persuade and move the people? In particular, how does he get Americans to alter their lives in ways that run contrary to all their experience and attitudes, to accept less, not more, to believe a genuine crisis exists?

Carter will have his audience now. After the frustrations and fears engendered by the gas lines, the rising prices, the specter of recession, the sense of fundamental changes ahead, he'll be listened to intently whenever he chooses to speak. And he will be examined and judged even more critically for what he has to offer when he finally comes down from the mountain.

More words and declarations about a moral equivalent of war won't work. Something akin to wartime marshaling of the national will is required, but with specific goals established that citizen can understand and accept.

The ironies in this are compelling. From the beginning of his presidency, Carter has warned of the impending national energy crisis.

But he has been unsuccessful in getting the politicians and the public to accept his ideas and begin the long process of change.

He was speaking, but no one seemed to be listening. Then, in recent months, the drumbeat of disastrous news struck the public bluntly and swiftly.

Iran'a collapse into bloodly, uncertain revolution sent a tremor throght the industrial world. At home, hysterical cries for America to "do something" sounded from all quarters. Even normally circumspect citizens were nervous. America's pride in its vaunted technology suffered a series of blows. Commerical airplanes cracked and were grounded. Nuclear plants became suspect after that ominous "bump in the night at Three Mile Island touched off alarms and sent radiocative clouds into the atmosphere. Our largest orbital space endeavor, Skylab, began plunging toward the earth, posing threats to life and limb worldwide. And then the gas lines, compounded by the latest OPEC price rise. Nothing was working.

Now the public, so critical of government in Washington and all its works (as was Carter), is looking to the captial and the president for strong action to solve the problems.

For Carter to convene his advisers in an atmosphere of crisis at Camp David also has its ironies. Carter campaigned to provide the most open of presidencies, yet it's his private deliberations, carefully sealed off from the public, that has been most successful. His latest secret meeting actually is Camp David III.

The first was in April 1978. He then summoned the leaders of his administration, in the White House and the Cabinet, for a weekend of soul-searching and self-examination. His presidency was in deep trouble, plagued by political mistakes, and a growing public perception of ineptness. In private, Carter was blunt. The American public was giving them low marks, he told his people, and he could understand why. They deserved them. The American people were diappointed in them, and should be. They had made many promises, and failed to deliver them. They had promised an energy bill that first year, and hadn't achieved it. They had promised other reforms, and hadn't fulfilled them. They simply hadn't done as good a job as they should. It was time to straighten up, pull themselves together, and perform as they were capable.

When he privately breifed congressional leaders on that meeting, the president said: 'We've had some problems that needed clarification after 15 months in office. We were green. And so I spent two days at Camp David in very intimate, frank, brutal, discussions. And we've made some progess.

Camp David II, the celebrated days alone with Anwar Sadat and Menachem Begin that led to the singing of the Israeli-Egyptian peace treaty, followed some four months later. But Camp David III, now in progress, could be the most critical of all.

Other presidents have turned dramatic moments to their advantage -- FDR with his famous "garden hose" speech giving aid to Britian before World War 11, Kennedy at the missile crisis, LBJ in his "we shall overcome" speech after Selma. Mixon, not yet a president, saved himself with "Checkers." With Carter, the least inspring of the political figures, a speech alone won't do it. Action might. CAPTION: Picture, Mondale, flanked by Carter aide Jack H. Watson Jr., left, and Kentucky Gov. Julian Carroll, is applauded after speech.