Democratic political insiders differed widely yesterday about how severely Massachusetts Gov. Michael S. Dukakis' presidential campaign will be damaged by the disclosure that his staff sabotaged a rival candidate, and by the way he handled the episode.

But they agreed that the cumulative effect of the crises that have hit the Democratic field this year, and already destroyed the candidacies of Gary Hart and Sen. Joseph R. Biden Jr., have soured their party's prospects for winning the presidency next year.

"The soap operas can't go on if we're going to win the White House," said Democratic pollster Geoffrey Garin.

"It's like a bad dream that started about five months ago and hasn't ended yet," said Robert Beckel, 1984 campaign manager for Walter F. Mondale. "We keep saying these are isolated incidents, but you can't have this much bad news in such a short time and there not be a fallout."

"In the public mind, running a campaign becomes a metaphor for running a government," said pollster Andrew Kohut, president of the Gallup Organization. "The problem is that these kind of episodes reinforce the impression in the public's mind that Democrats can't manage things."

"It takes the sleaze issue away from us," added one surviving 1988 campaign manager, who asked not to be identified, "and that hurts."

Several observers said they viewed yesterday's disclosures as a grave wound to the Dukakis campaign because they went to the heart of the two qualities on which he has built his reputation: competence and integrity.

"The damage is hard to measure, but Dukakis' problem is that his campaign theme is management and innocence, and here's a guilty campaign that's out of control," said Robert Squier, a Democratic campaign consultant. He added that Dukakis made matters worse by not making a clean break with his campaign manager, John Sasso, once he learned Sasso had put together the "attack videotape" that led to the undoing of Biden's campaign. "It would have been better if it hadn't been so wobbly. He should have just fired him."

David Garth, a New York-based Democratic consultant said, "It may not be officially over {for Dukakis} but it's going to be. I don't think you survive this kind of thing in the current climate. If the press forced out Joe Biden, the press is going to force out the guy who did it to Biden. Even though Dukakis says he didn't do it himself, it happened on his watch."

Others said, however, that the initial act of sabotage was not likely to be judged too harshly because it was not a bona fide dirty trick, but rather fell into a gray area of trafficking in negative information.

"The regrettable incident over the Biden videotape needs to kept in perspective," said Democratic National Chairman Paul G. Kirk Jr. "As far as I can tell, no one charged one campaign with lying or spreading false information about another . . . . This fact in no way excuses Gov. Dukakis' campaign manager of his actions. It was a tactic which I do not condone."

"I don't think this will have a serious lingering effect on Dukakis," said Robert Neuman, an aide to Rep. Morris K. Udall (D-Ariz.). "Among campaigns it is recognized that politics ain't beanbag, and there is even some respect for those who play hardball."

"Dukakis will be unhurt," said Ted Van Dyk, a veteran party activist who had been a Hart adviser. "He dealt with it in 24 hours, and there was no attempt to hide it."

Biden yesterday sidestepped the controversy. "What's done is done," he said in a statement. "As I said last week, it's time for me to move on. All my energy and focus are on the Bork nomination."

While many in Washington said Sasso's biggest mistake was not the preparation of the tape, but the subsequent cover-up, activists in Iowa, scene of the nation's first caucus Feb. 8, took a sterner view.

"The standards of fair play are higher in Iowa than elsewhere," said Iowa Attorney General Tom Miller, a supporter of Democratic presidential hopeful Bruce Babbitt. "In some places an attack video is an expected part of the political process. Here, Democrats frown on negative campaigning. Our standards are simply different than in Massachusetts, New York or California."

He added that many in his state were especially angered by timing of the leak. "It's one thing to put obstacles in front of an opponent, but it is quite another to damage the chances of derailing the Bork nomination during the middle of confirmation hearings by degrading the chairman of the Judiciary Committee," Miller said.

Several sources said that Dukakis' most severe damage will come not from public reaction, but from the loss of Sasso, his right-hand man, and Paul Tully, his staffer with the deepest background in presidential campaigning. "It's as though they've lost the central computer and the brain, and I don't know if you can replace that," said one Democrat who asked not to be identified.

Beckel noted that, like Biden, Dukakis is handicapped because the public does not know him yet, and this flap will be part of its introduction. "The timing could not be worse," Beckel said. "Here is a guy with a lot of momentum, who's raised a ton of money, and it seemed like he had an open field ahead of him. This is a fast way to slow that down."Staff writers Bill Peterson and James R. Dickenson contributed to this report.