A NAGGING question for reporters this week, as the Congressional Iran -- contra investigation concludes with a final report, is why the U.S. news media missed the biggest story of the Reagan administration.

When "that rag in Beirut," as President Reagan called the Lebanese weekly Ash Shiraa, wrote that the administration was dickering with Iranian "moderates," all but a few journalists were surprised. And when Attorney General Edwin Meese III stepped up to the podium in the White House press room last Nov. 25 and told about how Iran profits had been rerouted to the Nicaraguan contras, reporters were stunned.

How did such a big story tiptoe almost silently past the most powerful media establishment in the world?

The Iran-contra story offers an unflattering portrait of how the news media does business in the 1980s. Today's news organizations are big and brassy, peopled by reporters who snarl questions at the president. But these same organizations are far more timid than they sound. Media conglomerates can be as slow and bureaucratic as the Department of Agriculture; gruff editors can be softened by administrative favors and cowed by administrative criticism. Reporters and editors are so busy focusing on the fast-breaking news that the important time-consuming stories can get away from them.

Uncovering the Iran-contra affair wouldn't have been easy -- even for the best of journalists. One tentacle stretched to the iddle East, where arms were traded secretly for hostages while President Reagan talked publically of "swift and effective retribution against terrorists." The other tentacle was in Central America, where Lt. Col. Oliver North was pulling the strings on a contra-support operation at the same time Congress had banned such support, directly or indirectly.

Here are some of the reasons why these two strands of the Iran-contra tale kept getting lost:

Coziness with sources. Some journalists were coopted by the very people who were doing the dirty work. Some depended too much on National Security Adviser Robert McFarlane to tell them what his office was doing. Ollie North mesmerized some journalists who dealt with him on a regular basis. As one newspaper reporter who fell under North's sway confesses now: "North regarded the media as a tool to be used."

Time pressure. Journalists were busy, and their editors were impatient. The media has a short attention span, and Iran-contra was a complicated, long-term story that would tie up investigative teams for months. Other news that was easier to cover also seemed more important -- things like budgets and mid-term elections and the Libyian air raid.

False bravado. For all the shouting across the White House lawn and the hardball questions asked by stern-faced television reporters, the news establishment has been a lot softer and more malleable than it appears. The Reagan era brought on a period in which the media were wary of seeming too confrontational; showing the flaws of a popular President made a reporter, and more important, his editor, unpopular. In an ideal newsroom, such things don't matter. But as one New York Times reporter notes, when some reporters had their facts challenged and their motives questioned by the administration, they simply grew weary of bucking the system.

Changing standards. Investigative journalism, given a boost by Watergate, seemed to change in the 1980's. It was still a way to win prizes and journalistic approval, but in recent years, some news managers grew wary of endlessly searching for bad guys and tilting at windmills. Some investigative reporters at The Washington Post and other newspapers turned to in-depth explanatory reporting on social issues. The Iran-contra story served to remind newspapers why investigative reporters should investigate, not merely explain.

National-security jitters. The press has come a long way from the get-it-print-it mentality of the 1970's. Many newspapers, including The Washington Post, are now more willing to hold stories for a day or longer to listen to the arguments from the government about whether the story will damage national security or endanger American operatives abroad. These issues are always tough ones for reporters and editors, but in the case of the Iran-contra affair, there was the added question whether stories would harm the hostages in Beirut. The fear of jeopardizing innocent Americans kept some stories frozen deep in news computer systems. At the Associated Press, this fear had a very human face -- Terry Anderson's, the AP Beirut bureau chief who was taken hostage in March 1985.

Looking back, there were several stories that should have raised warning flags for reporters covering national security, the Middle East and even the White House. Some of the stories surfaced outside the establishment papers, magazines and networks. For many journalists, the question was: If it's such a good story, why haven't any of the big guys confirmed it?

On the issue of arms for hostages with Iran, there were a few early signals. Time magazine in July 1983 told of military equipment going to Iran through Israel, but the story seemed to disappear, even in Time magazine. John Wallach, foreign editor of Hearst Newspapers, wrote in July and September 1985 about a "mutual desire to improve relations with Iran," noting Iran's need for arms and the U.S. efforts to get back the hostages. In January 1986, he told of arms going to Iran through Israel. And in April 1986, Jack Anderson and Dale Van Atta reported a tilt toward Iran and said that the CIA had given approval for arms sales to Iran through Israel.

Wallach, whose articles were published in various cities -- but not Washington or New York -- said that his stories were met with vigorous denials from the White House and from then CIA director William Casey. For many other reporters, the denials were enough.

"In the wake of all the denials, I just stopped covering the story," Wallach said.

At an Investigative Reporters and Editors convention last summer Michael Wines of The Los Angeles Times said he talked to a source in 1986 who suggested he read Van Atta's columns "and I went back and told my editors and never even bothered to look them up. So mea culpa, mea culpa, mea culpa."

Wines also said that the LA Times "put one of the best reporters in Washington, Doyle McManus, on the case" who spent two months and came back and said, "'Frankly, Mike, I think your source doesn't know what he's talking about.'"

McManus, who later teamed up with Wines and broke some of the major stories on the Iran-contra investigation, recently acknolwedged that "I just came up with a lot of dry holes. The irony of it was that my sources turned out to be the people (in the government) that this was being kept from."

Newspaper editors had trouble keeping the story on page one -- even when they sensed the outlines of the scandal. Several publications, including The New York Times, The Wall Street Journal and The Washington Post, published articles suggesting the role of North and the NSC in questionable activities. These proved to be what journalists call "black hole" stories, which blaze for a moment, hit some important target and then -- for mysterious reasons -- disappear. Reporters and editors didn't want to seem unfair, and they didn't want to make a nuisance of themselves in the way that would have been necessary to focus public attention on the storyu.

New York Times reporter Joel Brinkley said last summer that "every time we'd write one of these stories, the White House would simply offer bald-faced lies and accuse us of being pro-communist. Maybe, I shouldn't care about that. . .but {eventually} it just wears you down . . . . There begins to grow a seed of doubt in the minds of some editors. What is this? Is Brinkley really right? What's this about? That's not a good explanation, but I'm human, and I did not follow up."

The case of Eugene Hasenfus, the pilot whose plane crashed in Nicaragua in October 1986, was another example of a story that tantalized with its possibilities and then disappeared. Bob Woodward, The Washington Post's assistant managing editor for investigative stories, said that when Hasenfus crashed, Post Managing Editor Leonard Downie Jr. said, "'Let's get out and plow the fields on this story.'" Woodward blames himself because "I didn't get out and plow the fields."

At Newsweek, Christopher Dickey in Cairo and Rod Nordland in New York began picking up "little pieces of the story" about arms sales to Iran in the summer of 1985, according to Richard Sandza of Newsweek's Washington bureau.

After three months of reporting, Sandza said that Newsweek reporters "had a pile of documents maybe three feet high" but no first-hand evidence of the arms for hostage deal. "Our accounts were from guys in jails, drug runners, sleazeballs, the lowest form of humanity and we just decided that we didn't have a story," he said.

Sandza also said one Newsweek reporter "was being quietly briefed about U.S. efforts to win back the hostages" which included much of the detail that would come out later. But the reporter got the briefings on the understanding that Newsweek would not write until the hostages were released.

"In this case, if hostages lives were at stake, who's going to write the story and jeopardize their lives," said Sandza. "But the fact was that we had the biggest story of the decade in one of our reporter's notebooks."

Of all news organizations, the one with the toughest predicament was the Associated Press. AP's Beirut bureau chief, Terry Anderson, had been taken hostage in March 1985, and AP executives were trying to work with the government to help get Anderson out. Their main contact during a key period in 1986 -- Lt. Col. North!

So how did the AP investigate North? Two former Associated Press reporters who were working on North's connection to the contras -- Robert Parry and Brian Barger -- believe that their stories were spiked, delayed and defanged by AP editors out of a false sense of protection for Anderson.

"AP, like the government, said the hostages would not change how we would handle the news and yet I think the evidence was that we did," said Parry, who now works in the Washington bureau of Newsweek. (AP President Lou Boccardi denies that the AP softened, delayed or spiked any stories about North because of their dealings with him.)

When the Miami Herald published a story that Parry felt he had been prevented from pursuing, Parry said he raged at the editors, saying: "You have just given The Herald a Pulitzer."

The June 1986 story, by Alfonso Chardy from the Herald's Washington bureau, said that despite congressional restrictions "the Reagan administration has continued secretly to assist anti-Sandinista rebels...through a network of private operatives overseen by the National Security Council and the CIA...." It included new detail about how North was maintaining his connections to the contras, and it was one of the reasons The Herald did indeed win the Pulitzer this year for its Contra coverage.

The Associated Press was far from alone in maintaining contact with North. North, who dazzled reporters with his version of his war record, talked regularly with journalists who covered national security. He gave them information and guided them on stories. He also gave them misinformation and used them to pursue his cause.

"I call it journalistic immunity," Newsweek's Sandza said at the investigative reporters convention last summer. "People who help you out, you just don't mention their names unless it is absolutely necessary."

North in fact went to great lengths to make certain his name was not mentioned, even when he had become a key element in the story. When articles were being written about North's efforts for the Contras in the summer of 1985, North and his boss, McFarlane, telephoned news organizations and pleaded that North's name be kept out of the public domain for fear he would be a target of unnamed terrorists.

Some journalists, citing lack of subpoena power and other official investigative techniques, blame the Congress instead of the press for falling down in pursuit of North's raiders.

But Congress's failure to investigate doesn't absolve the media, any more than does the fact that the administration lied or hid the truth. A reporter ought to do more than wait for an official arm of government to investigate or for somebody else to leak a story, although too many editors feel safer when stories come this way.

Eleanor Randolph covers the news media for The Washington Post.