The beaches and the mountains offer, this Fourth of July holiday, an even more telling symbol of the national spirit than usual. For Americans are into themselves these days.

To a rare degree, we have turned our backs on politics and public affairs. While that may not bode so well for the long term, right now all the most heralded troubles seem somehow to be taking care of themselves.

Jimmy Carter, of course, is the best sign of the flight from politics. Not only did he reach the White House by running against Washington, but once in office he had to scale down his plans for government action. Very little of his social legislation is getting anywhere, and on his two most important domestic problems - energy and inflation - he has been forced into the position of letting the private sector do most of the work.

Here in the state of surf and sun, the turning away from public affairs is particularly striking. The landslide vote in favor of Proposition 13, cutting property taxes and limiting all other taxes, says one thing very loudly. By a huge majority, people want to spend their money themselves rather than give it to the government. Gov. Jerry Brown may be liberal on minorities, nuclear energy, labor and the death penalty, but when it comes to talking up the private sector he sounds like Ronald Reagan.

The historians agree with the politicans in their assessment. Morris Dickstein, who wrote in "Gates of Eden" a fine and unusually sympathetic account of the 1960s, said of the present decade in an interview published by Encounter Magazine: "What's happened today in the United States is that essentially it's been depoliticized. We're now into one of our unpolitical phases . . . and people are not using politics so much as an avenue of personal fulfillment."

Because I depend on politics for material to write about, I can't adopt a wholly benign view of what's happened. But even self-interest flags before the strong evidence that some of the heavier problems tend to take care of themselves.

At home the economy has long seemed poised between recession and inflation. But heavy consumer spending, particularly for cars and homes, has sustained recovery and expanded job openings at a record pace. Signs now suggest that consumer spending is tailing off - just enough, perhaps, so that the country will be spared both recession and high inflation this year.

Abroad, the communists seem to be gaining ground at a great rate. But no one seriously believes the Russians are coming over the top in Europe. Africa doesn't count that much, and the Soviets may as easily be sorry as glad for being deep into Angola and Ethiopia.

In Asia, the dominant motif is competition between Russia and China now expanding into tension between China and Vietnam and between Vietnam and Cambodia. The domino theory, invented by the hawks to justify continued American presence in Vietnam, has been stood on its head. American absence from local conflicts there works for us against the communists.

Even that rheumatism of world affairs, the Mideast, isn't aching too painfully now. Despite the toughness of Prime Minister Menachem Begin and the supposed weakness of President Anwar Sadat, the Israelis and the Egyptians are talking. They're apt to keep talking if the United States - which now finds itself in better position than at any time since Carter came to office - doesn't get into the act too heavily.

Bright as the present may seem, however, the clouds are not going to stay away forever. Policy counts in economics. Unless the government works to curtail big wage and price hikes, inflation will take off. The non-political actions necessary to fight inflation - that is, monetary restraint by the Federal Reserve System - dampen spending and investment. So unless there is a tax stimulus, there will be a recession, and perhaps a bad one, sometime soon.

As to foreign policy, the United States and Russia cannot keep playing blindman's bluff indefinitely. At some point the absence of consensus in this country and the leadership issue in Russia will be resolved. They will both be resolved adversely unless Washington takes a position that makes assertiveness risky for Moscow and accommodation worthwhile.

So as we take our ease this weekend, there is reason for a tiny glimmer of doubt. This fair moment, in which doing nothing seems to be the best prescription for everything, cannot possibly linger long.