LAST THURSDAY, PRESIDENT Reagan's press secretary, Larry Speakes, gave away a state secret. "You don't tell us how to stage the news," he told White House correspondents, "and we don't tell you how to cover it."

It often seems to be just that simple. The news media do tend to leave it to the White House to stage the news, and this White House -- with a dramatic flair better than any since Nixon's -- stages good news. The fact that the drama is regularly as false as a television soap opera generally goes unnoted, particularly on television.

Do many Americans realize how the television networks and the White House now interact? Not likely. Last Monday and Tuesday, for instance, the White House director of communications, David Gergen, was on the phone with the Washington bureau chiefs of the television networks repeatedly, telling them much of what President Reagan planned to say in his "nonpartisan" campaign speech of Wednesday night. Gergen was trying to persuade them that the speech should be shown on the networks as a news event. White House spokesmen and network officials consider this sort of call routine. (Gergen said later he'd done it before, and Jody Powell, Jimmy Carter's press secretary, recalled going through similar motions while he was in the White House.) But an outsider could be forgiven for interpreting Gergen's efforts as extraordinary special pleading.

Consider the absurdities: The president has his man shop around for free television time on the grounds that he has something newsworthy to tell the country. So the president's man calls network news executives who -- sworn to keep the secret from their own reporters -- listen to a description of the speech the president proposes to give.

They then consult with their superiors in New York, who debate earnestly whether what they've been leaked constitutes "news." These are the same network executives who have assigned three correspondents and three camera crews to cover the White House at all times; who have authorized the expenditure of thousands of dollars to try to get telephoto shots of the vacationing president riding a horse; who put the president or his family on the evening news programs virtually every night of the year, no matter what he is doing. These executives have to decide whether a presidential address on the economy five days after the announcement of 10.1 percent unemployment and 20 days before a national election is news instead of politicking.

The networks' reporters seemed to have no doubts about the question. Bill Plante, the CBS White House correspondent, told his viewers repeatedly that the speech would be a repeat of the message President Reagan has been delivering on the political stump this fall. And moments after the speech was over, Plante told CBS viewers, "It's the exact same speech he's been giving on the campaign trail, minus the references to the Democrats." Thursday night on the Evening News, Dan Rather referred to "President Reagan's campaign speech last night." Chris Wallace, the NBC White House correspondent, said before the speech was delivered, "I don't think anybody is fooled" about whether it would be political or not.

Fooled or not, CBS and NBC both broadcast the speech live on the ground that it was not just politics but legitimate news. ABC, bravely, decided not to broadcast the speech. By the time he got on the air the President could abandon the charade, so he ended his speech by quoting the Republican Party slogan for this election year: "We can do it, my fellow Americans, by staying the course." It was one of the great "screw you" lines of recent American history.

Like any television show, the news programs have to have a star. The president is the ony personality who can play that role (besides the anchorman, of course). The entire system of reporting news in this country is distorted by the preoccupation with the White House. The newspapers are not immune. The lead story on page one of last Monday's Washington Post reported the news that President Reagan was convinced that the previous week's rally on Wall Street was a vote of confidence in the economy. Any such information conveyed by presidential aides to reporters is probably worth printing in a big newspaper like The Post, but as the lead story? (The Post also printed the text of Reagan's Wednesday night speech, treatment usually reserved for important policy statements. The Post printed a Democratic reply, too.)

In fact, presidents regularly get away with the public relations equivalent of murder. They turn erzatz into real, right before our eyes. Consider the spectacle of the president gruffly ordering a kooky California Republican to "shut up" in the East Room of the White House. Great stuff, right? Big items on the TV news; front page stories; a subject of discussion and commentary. Egad.

Richard Nixon mastered the art of pushing the media around. As people in television readily admit, a president who insistently repeats the same message when the cameras are his captive audience does get his message across, even if it is demonstrably false or ridiculous. Nixon did this on Watergate matters; Reagan does it on the economy.

And the television networks have a hard time reacting. They haven't found a formula for saying the president is wrong. Network executives, many of whom are genuinely thoughtful people, debate what their responsibility is. Howard Stringer, the British-born producer of the CBS Evening News, thinks the Democrats deserve much of the blame for letting Reagan get away with misstatements. "In America there isn't the mechanism of the loyal opposition" that can speak forcefully against the sitting president, he observes.

"One tends to try to avoid nibbling the president to death," Stringer acknowledges, adding: "You can build up a reservoir of backlash to network television" by criticizing the president regularly. The networks are sensitive about their own public images.

"It is reminiscent of the Nixon days," says Tom Brokaw, who was NBC's White House correspondent in the Nixon years and now coanchor of the Nightly News, "because he (Reagan) appeals to people who are naturally suspicious of what we do anyway."

"You start from in a hole," Brokaw said of efforts to challenge points made by this president, "because he is so believable."

Ordinary Americans aren't dumb, but they need help understanding complicated issues and disputes. Television often abandons any effort to establish what is true as opposed to false. Last week, CBS's Plante reported on Reagan's signing of a jobs bill that was sponsored in the Senate by Sen. Dan Quayle (R- Ind.). Plante reported that the White House angrily disputed charges that it initially opposed this bill. Then Plante quoted Quayle as saying the White House put roadblocks in the way of his bill all spring and summer. Whether "true or false," Plante told his viewers, charges that Reagan really opposed the bill keep coming up. But CBS did not take the time or effort to clarify this murky dispute.

Eric Burns of NBC reported the big rise in the stock market last Monday, ending with an interview with Alan Greenspan, a Republican economist close to the Reagan administration. Greenspan said that when the stock market rises, unemployment subsequently falls. The economist wouldn't predict a date, Burns reported, and wrapped up his report with this solemn sentence: "But, says Greenspan, unemployment does go down."

Greenspan's confident analysis is demonstrably false. There was a big stock market rally from the end of 1980 through the first half of 1981 that brought stock prices to exactly the level they reached last week. That rally was not followed by a fall in unemployment, but rather by its steady climb to the record 10.1 percent level reached this month. Neither NBC nor anyone else in the media looked into that parallel last week. Instead, we all let Reagan get away with his rosy interpretation that this stock market surge -- unlike the first one of his presidential tenure -- was bound to be followed by economic boom.

But we let him get away with much more than that. Look back at the text of that nonpolitical campaign speech Wednesday night. Reagan took full credit for reducing the rate of inflation, when every licensed economist in America would give most of the credit to collapsing oil and grain prices, worldwide recession and the Federal Reserve Board.

Reagan denounced government deficits as a grave evil: "I did not come to Washington . . . to further mortgage the future of the American people. . . ." He lambasted Congress for shunning his newly beloved constitutional amendment to balance the budget. And in all the media, this just passed by. No one even bothered to recall that this is the president who, by virtually eliminating the corporate income tax (to stimulate a boom -- remember?) and doubling defense spending, will give this country by far the biggest deficits it has ever seen.

Some simple facts: President Reagan promised a balanced budget by 1984, and will -- his own staff now reckons -- have a deficit of nearly $200 billion in that year. President Reagan said his tax cuts would stimulate the economy, but the economy has headed steadily downward since the first tax cuts came into effect. President Reagan says a boom is right around the corner, but business bankruptcies continue to rise, and newly out-of- work Americans continue to apply for unemployment benefits in record numbers.

There was a boom on the stock market in August and September of 1932, and President Hoover, then running for reelection, tried to use rising stock prices as an argument to vote Republican. But the market ran out on Hoover (not as lucky a president as Reagan), falling again in October -- as of course it may fall from now until election day. (Like last year's stock market boom, the one that occurred in the late summer of 1932 did not lead to recovery or reduced unemployment.)

Election seasons usually create an unreal atmosphere, and this one surely has. By the time Congress comes back to town for a lame duck session beginning on Nov. 29, we will be in a different world. It will feature a national economic crisis consisting of high unemployment, a collapsing agricultural sector, a fragile banking system and unprecedented federal deficits; a president who many of his own friends will think of as a lame duck anxious to get back to the ranch in California; and a lot of terrified politicians in Washington. Keep the TV on; it should be an interesting season.