A senior advisor to the suspended presidential campaign of Sen. John S. McCain acknowledged yesterday that the candidate and his staff made serious strategic mistakes in the weeks prior to the primaries on Super Tuesday.

Dan Schnur, who served as communications director for McCain's operation, said that when the organization "acted like a conventional campaign," it fostered an atmosphere which destroyed McCain's quixotic bid for the presidency.

Schnur spoke yesterday at the Kennedy School of Government in an informal luncheon co-sponsored by the Institute of Politics and the Shorenstein Center on the Press, Politics and Public Policy.

"We made three major mistakes, and a million little ones," Schnur told a crowd of more than 50 students, faculty and staff.

The first major mistake, he said, was a series of television advertisements comparing Texas Gov. George W. Bush to President Clinton, which aired in South Carolina prior to the state's

Feb. 19 primary.

In the advertisement, McCain addressed voters about his Republican opponent, saying, "his ads twist the truth like Clinton. We're all pretty tired of that."

Schnur said that the segments, though quickly withdrawn by the campaign, did significant damage, disillusioning voters who thought McCain was "different from the others."