The political dust-up that cost two key aides their jobs with the Dukakis-for-president campaign this week grew out of a mutually beneficial exchange between reporter and campaign aide that is typical of modern American politics.

Dukakis's alter ego and campaign manager, John Sasso, and political director, Paul Tully, quit the campaign because of their part in passing out information about a rival candidate to reporters covering the campaign.

But instead of the normal transaction of a kind that happens virtually every week in a campaign season, this one went out of control in ways that Sasso -- the originator -- says he never intended.

The story began, according to the Dukakis camp, with a routine conversation between Sasso and New York Times reporter Maureen Dowd. (Dowd was out of the country this week and could not be reached.)

Sasso apparently expressed surprise to Dowd that no reporter had pointed out how Sen. Joseph R. Biden Jr. (D-Del.) had used a long passage lifted almost verbatim from British Labor leader Neil Kinnock in his dramatic close of an Iowa candidates' debate in late August without crediting Kinnock.

An official of one campaign planting an idea that might be damaging to a rival is routine, according to numerous reporters. Readers of The Washington Post have read the fruits of such suggestions in recent weeks -- for example, in a story picked up from the Milwaukee Sentinel that quoted Senate Minority Leader Robert J. Dole (R-Kan.) as saying someone ought to consider "blowing away" Nicaraguan President Daniel Ortega. The story was brought to The Post's attention by aides to three of Dole's rivals for the Republican presidential nomination.

Syndicated columnist Jack Germond of The Baltimore Evening Sun apparently got the same tip. "That morning pretty early I got a call from this guy who said, 'Have you read your Milwaukee Sentinel yet?' and I said, 'Well, no, haven't gotten there yet. What are you talking about?' " Germond recalled in an interview. He, too, wrote the Dole story after finding the Sentinel story.

In the original Dowd-Sasso conversation, Dowd asked whether Sasso could provide concrete confirmation of the alleged episode of Biden plagiarism, according to the Sasso version, and he then asked an intern in the Dukakis press office to prepare a videotape containing clips of Kinnock and Biden delivering virtually the same passage.

At this point the story took another turn familiar to political reporters. For reasons not fully explained, the Dukakis camp decided to send copies of the tape not only to Dowd at The New York Times, but to NBC News and The Des Moines Register.

On Sept. 12, all three organizations used the story, though in different forms. Dowd's story appeared on the front page of The Times, pointed out the plagiarism but did not mention that a Biden rival had tipped her off. On NBC, Ken Bode broadcast the story on the Saturday nightly news program, showing pictures of Kinnock and Biden that were even more devastating than the printed version. NBC also did not mention the source of the tip.

David Yepsen of the Des Moines Register handled the story differently. He wrote that he was able to compare Biden and Kinnock because he had received what he called the first "attack video" from a rival campaign.

Yepsen's story gave the Biden camp an opening it quickly seized. His aides told the legion of political reporters who jumped on the story that Saturday that their man had been clipped unfairly by a Democratic rival who failed to mention that Biden had been using the Kinnock material regularly in his speeches and nearly always giving full credit. The unidentified rival apparently wanted to sabotage the chairman of the Senate Judiciary Committee just as he was beginning a grueling few weeks as the Demcratic point man in opposition to Reagan's Supreme Court nominee, Robert H. Bork, Biden aides complained.

This line did not work when Biden was confronted in the days that followed with new and more damning cases of plagiarism. With speed that must have stunned the Dukakis camp, Biden was driven out of the race by a sequence of events that began with that Sasso-Dowd conversation.

Something similar, though less consequential, happened to Elizabeth Hanford Dole because of a rival campaign. Dole had spent much of her time this year flying around the country as secretary of transportation but making appearances and speeches that many Republicans interpreted as boosts for her husband's presidential campaign. Sources with access to her private schedule who were sympathetic to one of Sen. Dole's rivals for the Republican nomination leaked details of her travels to The Post and to the Evans and Novak column. Within days after a column and a front-page story appeared, Dole had resigned from the Reagan Cabinet to work full-time for her husband.

The Post's story on Dole's travels did not mention the original leak from a rival Republican camp.

How was Sasso's transgression different? According to many political consultants and political reporters interviewed this week, the differences were the timing, the contradiction between the leak and the themes of openness and honesty emphasized in Dukakis' campaign, and the fact that Sasso, Tully and others reacted to the furor the leak created by trying to cover it up.

"I think what makes it different is the goal," said John Reilly, a key senior adviser for Walter F. Mondale's 1984 Democratic campaign for the presidency and who was a political adviser to Biden this year. "The goal was to bring down the chairman of the Judiciary Committee at a time when there were some of the most important hearings in our history."

Some political reporters discounted the timing as "unfortunate," as one put it, and said that if a mistake was made, it was that Sasso ducked numerous reporters' calls on the subject in recent weeks, while Tully denied to Time magazine last week that the Dukakis camp leaked the tape. Then after the Time story appeared, Dukakis held a news conference Monday to deny that anyone in his campaign had provided the information that helped push Biden out of the race.

"I think the Dukakis people made a big mistake," said CBS reporter Eric Engberg. "Why didn't they stand up and say, 'Hey, we're running a political campaign and when an opponent does something wrong, we're going to talk about it.' "

If political campaign workers stop gossiping with reporters about what their competition is up to, "it's going to be pretty tough going for us political reporters," Engberg said.

The news organizations involved in this episode indicated that they agreed with Engberg by the way they protected their source for the Biden-Kinnock story. Yepsen may have been under the most pressure, because of his acknowledgement that the "attack video" came from a Biden rival.

Several news organizations including CBS named Rep. Richard A. Gephardt's (D-Mo.) campaign as the possible source of the videotapes. As a result Gephardt spokesman Mark Johnson pressed New York Times Washington bureau chief Craig Whitney to confirm that the Gephardt people were not involved. Whitney complied by telling The Associated Press Sept. 18, "They {the Gephardt campaign} did not plant any Biden story on The New York Times."

Some journalists were surprised that Whitney would issue such a denial, since it eliminated one of only a few possible sources and opened the door to further queries about the other Democratic candidates.

Time magazine this week said that a Des Moines Register staffer "involved in the preparing of his paper's story" told colleagues that their video was supplied by the Dukakis campaign, but Yepsen and his editors refused to confirm that. Even after Sasso admitted Wednesday that he was the original source, Whitney of The Times declined to acknowledge that he was.