John Sasso's return to the presidential campaign trail restores Michael Dukakis' link with a personal and professional alter ego who gave life to the Massachusetts governor's quest for the White House.

Sasso, 41, is a master tactician and organizer who brings his skills to the campaign he launched. That campaign has floundered in recent weeks in the face of attacks by Vice President George Bush on issues from Boston Harbor pollution and the Pledge of Allegiance to Dukakis' overall fitness to serve.Although Sasso's title of vice chairman theoretically makes him part of an inside troika - with national chairman Paul Brountas and campaign manager Susan Estrich - the elation among Dukakis loyalists that greeted his return indicated his role will be preeminent. Sasso resigned Sept. 30, 1987, after admitting responsibility for an "attack video" that eventually destroyed the presidential bid of Sen. Joseph Biden, D-Del.

Compounding the damage was Sasso's initial denial of responsibility for the videotape showing Biden had used, almost word-for-word, portions of a speech by British Labor Party leader Neil Kinnock.

The incident created a firestorm that almost consumed Dukakis, who has set high ethical standards while proclaiming his distaste for negative campaigning.

A chastened Sasso admitted Friday to an "error in judgment" and pledged to adhere to Dukakis' high standards. But he insisted "there are contrasts and weaknesses that are issues in the campaign . . . and I would not shy away from pointing those contrasts out."

But the 41-year-old political operative, who ran Geraldine Ferraro's 1984 vice presidential bid, quickly displayed his once-and-future role in responding to a Massachusetts Republican's suggestion he was "chairman emeritus of the sleaze factor in American politics."

"The information I provided was absolutely truthful and accurate and there was absolutely nothing unethical or illegal about what I did and that's a far different cry from what has gone on in many quarters of the Bush-Reagan administration," he said.

Dukakis and Sasso forged their bonds during the candidate's darkest days following his shattering 1978 gubernatorial primary loss. The two worked closely to build the foundation that resulted in his triumphant return to the statehouse in 1982.

Sasso also was the architect of many of Dukakis' legislative successes, carefully building coalitions among seemingly antagonistic groups.

It was Sasso who set the stage for Dukakis' national run, nuturing the idea during the 1986 re-election bid and encouraging him to begin the explorations that convinced the governor to run.

Dukakis initially refused to accept Sasso's resignation, then gave in when faced with mounting criticism over his apparent inability to make a decision.