IMAGINE (if you can) an America in which 55 percent of all black children are born out of wedlock, nearly all in poverty; an America that graduates illiterates from high school; an America that owes more to foreigners than foreigners owe to it; an America whose most successful manufacturing industries are steadily declining; an America with 35 million citizens living in poverty; an America whose president catches catnaps in cabinet meetings, and who once said that the nuclear-tipped missiles on our submarines can be fired and then recalled.

Imagine all that if you can, and you have imagined Ronald Reagan's America, or at least a version of it.

Now look at a Ronald Reagan commercial on television. "It's morning again in America," the suburban lawns are in perfect trim, the children all laugh, the American flag brings tears to your eyes, the sun is always shining, the feelings are universally warm and good. "Greatness lies ahead of us."

Is the commercial totally out of touch with reality? No, provided we understand that "reality" is sometimes intangible -- as intangible as a mood, for example. The Reagan campaign is exploiting a real mood in the country, a mood of relief and hope that somehow all the old problems that tore at our social fabric for 20 years will now disappear. It is always easier to believe what we want to believe.

In some of its moods, this country is indifferent to facts. Consider the Reagan record on deficits. He began his administration with a solemn admonition about the national debt in his first state of the union address, warning that a trillion dollar deficit meant the ship of state was "out of control."

"A trillion dollars would be a stack of $1,000 bills 67 miles high," the president revealed in his first dramatic television address to the nation.

Less than four years later the national debt is $1.57 trillion. That stack of $1,000 bills is now 105 miles high. The Reagan administration has yet to propose anything remotely resembling a balanced budget. Instead, it has proposed a constitutional amendment requiring a balanced budget. The administration's much-ballyhooed cuts in government spending will save less money that it will cost to make the interest payments on the new Reagan- era national debt -- which we will now be paying for generations. But who is laughing at this record?

Or consider relations with the Soviet Union. During the 1980 campaign Reagan promised his countrymen that a rapid buildup of American arms would force the Soviet Union to bargain seriously on arms control. He initiated the buildup, but for four years the Russians never succumbed to his blandishments. As recently as last December, the president's national security adviser, Robert (Bud) McFarlane, told an interviewer: "I am persuaded that 1984 must be a year of careful, reasoned discourse between the Soviet Union and the U.S. I expect that it will be." But it wasn't.

Then Thursday night Vice President George Bush assured us that when Reagan recently met Soviet Foreign Minister Andrei Gromyko the president was "excellent, right on top of that subject matter."

"And I'll bet you," continued Bush, "that Gromyko went back to the Soviet Union saying, 'Hey, listen, this president is calling the shots, we'd better move!'"

But almost no one laughs at this foolishness either. The country seems disinclined to vote Reagan out of the White House over matters like these. Despite the excitement of last Sunday's debate and the new "age issue," a Reagan victory on Nov. 6 still seems by far the most likely probability.

If Reagan is re-elected, it seems fair to conclude that a majority of voters wants more of "the same." This does not refer, of course, to the worst recession since the Great Depression, which the Reagan administration brought us in 1981-82, nor to the Lebanon fiasco, nor indeed to much of anything very specific. As the pollsters have told us all year, many voters who disagree with Reagan on specific issues nevertheless plan to vote for him. They are people, it appears, who want the current mood to last, who like Reagan's "leadership" and who don't want an old-time Democrat like Walter F. Mondale back in the White House. A presidential election, after all, requires voters to choose between two human beings, not two ideals.

But what is the likelihood that Reagan can prolong the mood of this Olympic summer and placid autumn, when the Chicago Cubs (!) nearly made it to the World Series? Can a second Reagan term really duplicate the happy final year of his first? The chances of that seem remote.

Reagan was warned fully eight months ago in this Outlook section that his second term could be disastrous if he didn't begin at once to make creative plans for it. "Presidential power and authority are cruelly ephemeral," wrote David Gergen, who at the time had just resigned as Reagan's director of communications. Noting the political collapse of both Lyndon B. Johnson and Richard M. Nixon after they won landslide re-election victories, Gergen wrote that "Reagan himself is not immune to a fall."

Gergen proposed that the White House assemble some creative outsiders who could come up with original plans for dealing with the the huge problems that Reagan will face in a second term. As far as we know, his advice was ignored. Reagan himself appears to have no concrete plans for the next four years.

In his debate with Mondale, Reagan was asked: "What is your program for America for the next decade, with some specificity?" He replied:

"Well, again, I am running on the record." The only thing he would say about the future was "we'll continue to try and get things that we didn't get" in the first term, though in other answers -- on Social Security, for example -- he contradicted even that vague answer, insisting that he has abandoned his earlier proposals for cutting the Social Security program.

At Bowling Green University late last month, a student asked Reagan, "What do you want the American people to remember most about your presidency?"

He would be pleased, Reagan answered, "if they would just be able to say, I gave the government back to the people."

It's a revealing answer (one Reagan has repeated several times). It has nothing to do with classical presidential ambitions -- it implies no monument to Reagan's creative use of government power, no peace treaties with foreign adversaries, no affirmative accomplishments at all. This president, as he has demonstrated again and again, has little interest in using the government to improve the world or the country. He only wants to diminish the government as a force in our lives.

So far, Reagan has had more luck reducing the government's presence in his own life. "Big government" is still with us -- it's bigger now as a percentage of gross national product than it was under the hapless Jimmy Carter. But our president has mastered the arts of government-at-arm's-length and government-from-9-to-5. The relationship between his own version of what goes on in this country and the reality of our national life seems purely circumstantial.

Reagan has formidable powers of denial. When things happen that displease him, he simply denies that they happened. John M. Berry of The Washington Post gives numerous examples of this proclivity in today's Business section, citing errors of fact Reagan made in last Sunday's debate.

Challenged to explain why his campaign promise to balance the budget was not kept, Reagan claimed he had abandoned that promise even before the 1980 election, but in fact it was included in his March 1981 economic plan. Reagan claimed that after adjusting for inflation, spending on domestic programs in his administration has not increased at all; in fact, it has already increased by 6 percent. The increase in poverty during his administration had nothing to do with domestic budget cuts, Reagan said. Independent studies have demonstrated otherwise. "We have more people receiving food stamps than were ever receiving them before," Reagan asserted. In fact, the number of recipients fell from 20.7 million in January 1981 to 20.3 million last July, despite an increase in poverty.

We have, in Calvin Trillin's felicitous phrase, a "disengaged president" (comparable to a "disengaged blonde" or 10- pound "disengaged-bells," as Trillin put it.) There was a bizarre example of that in the debate, when Reagan told this story:

"In California, some time ago, a man beat a woman so savagely that the unborn child was born dead with a fractured skull. And the California state legislature unanimously passed a law (making such a crime murder) that was signed by the then- Democratic governor."

Reagan had an accurate recollection of the event and the law, but not of the governor in question. That new law was signed, not by some Democrat, but by Gov. Ronald Reagan. Reflect for a moment on the memory that can make that kind of mistake.

The evidence of Reagan's failure to master the basic subject matter of his job is now overwhelming. Strobe Talbott's brilliant new book on arms control in the Reagan years, "Deadly Gambits," demonstrates that the president is as blithely ignorant of arms control issues as he is of economics. Not only did he once observe that submarine missiles can be recalled after they are launched (an impossibility), Talbott reports, Reagan also told a group of congressmen in 1983 that "land-based missiles have nuclear warheads, while bombers and submarines don't."

For a long time Reagan remained magically invulnerable to criticism of his competence, but that has now changed. The behavior of the news media since last Sunday's debate has been remarkable, and instructive. Once his performance in the debate raised questions about the degree to which Reagan is still with it, the media opened fire on him. "Reagan's debate performance invites open speculation on his ability to serve," headlined The Wall Street Journal in a devastating front-page story last Tuesday. The television networks and other newspapers quickly followed with similar pieces. The White House had to release new details of the president's last physical exam to try to counter the unexpected "age issue."

Many members of the White House press corps have been frustrated by their inability to fully describe the Reagan they feel they have gotten to know in the last four years. In interviews just before last Sunday's debate, several of these reporters commented on the country's apparent indifference to stories about the presi=nt's factual errors, his isolation and his disengaged approach to this job. But a genie came out of its bottle after that debate. Even if he wins re-election, from now on, Reagan's foibles will probably get more attention -- and more of a public response -- than they did during the first term.

This is one of the reasons why a second term is likely to be considerably different than the first. In fact, we can already see new political factors that could transform the Reagan presidency after Nov. 6 even if he wins re-election comfortably. Not all of these things will happen, but some of them are bound to.

One new factor is an inevitable consequence of a lame-duck presidency. The Republican Party, ripe for deeply divisive political warfare, may not hold together in a second term as it has in the first. The extreme conservatives, the religious right, the traditional conservatives and moderates in the GOP could join in open combat once jockeying begins to see who will control the post-Reagan party. All these factions are represented in the Reagan administration, and even in the White House staff. Their open warfare could paralyze the administration on important issues like new taxes, arms control and Central American policy.

The greatest source of political energy in Washington in a Reagan second term could be the Republican-controlled Senate. Every Republican senator will realize after Nov. 6 that his committee chairmanship and majority status will be hanging in the balance: 22 Republicans will be up for re-election in 1986, and a dozen of them look vulnerable already. If only a handful are beaten, the Democrats are likely to regain control of the Senate.

This prospect will terrify -- and mobilize -- Republican senators. But they will be without their adept leader, Howard H. Baker Jr., who is retiring to run for president in 1988. Republican senators will face pressures from the far right that was so evident at the GOP convention in Dallas, and which wants action on controversial social issues; and they will face pressures from Wall Street and the business community, whose fear of the huge federal deficit can be expected to grow in intensity. A donnybrook is possible.

And of course, the present rosy calm at home and abroad is most unlikely to last another four years. The economy has so thoroughly baffled our economists that most now acknowledge their inability to foresee its future, but the combination of the biggest budget and trade deficits in our history and a seriously overvalued dollar does not suggest stability for the long term.

In foreign affairs, the crises in Central America remain perilous, and there is a very real possibility that the fragile set of arms control agreements that still restricts both Soviet and American arsenals could collapse in the next few years. Instability in both Syria and Israel seem inevitable. The Philippines are on the verge of traumatic upheaval.

Those happy-talk Reagan campaign commercials so pleasing to eye and ear are easily misunderstood. At first blush they appear to appeal to our confidence about the future, but actually they play on our insecurities. Like Reagan himself, the commercials slide over the real complexities of our age, assuring us that we don't have to worry about black children born out of wedlock, or declining schools or the perils of nuclear weapons and revolution in the third world.

America was traumatized during the 15 years from the beginning of the Vietnam War to the seizure of our hostages in Iran. Ronald Reagan has offered to end the trauma and return us to a happier, simpler condition. Most Americans, apparently, welcome the Reagan balm, even if a lot of them fear that it may be snake oil. This feels good, while it lasts.

The Reagan commercials are also misleading in their vagueness; they don't seem to make any promises about the future, as the Democrats have complained. But in fact they make a big promise, albeit unspoken -- they promise implicitly that the future will be rosy, if only we stick with Reagan. But this is a promise that probably cannot be kept.

When the magic is broken, we will have a new politics in America. This year the talk has been of a great conservative realignment, but that is most unlikely.

Political tides in this country seldom run very deep. The Americans who decide most elections -- the swing voters who in recent years have voted for Dwight D. Eisenhower, John F. Kennedy, Lyndon B. Johnson, Richard M. Nixon, Jimmy Carter and Ronald Reagan -- are a fickle lot, as that list confirms. If this year they again vote for Reagan, next time events may push them in a different direction.

If it's really morning again in America, how long can morning last?