Atty. Gen. John K. Van de Kamp, co-author of a rival insurance initiative, denounced an insurance industry proposal to cut lawyer contingency fees as "the most expensive lawyer-bashing campaign in state history." Speaking in Monterey at the annual convention of the State Bar Assn., which governs the conduct of lawyers, Van de Kamp said the insurance industry's Proposition 106 on the Nov. 8 ballot "is not a serious attempt to protect consumers." Instead, he termed it a "ploy to gain the advantage over people who wish to make accident claims against insurers." Proposition 106 would sharply reduce the amount that lawyers can take in contingency fees when their clients win suits against insurance companies. Van de Kamp is a backer of Proposition 100, sponsored by the California Trial Lawyers Assn. and intended to reduce insurance costs. There are five insurance-related measures on the ballot.