At a time when the public is being assaulted with unsolicited e-mail ads, California is about to launch the toughest counterattack in the nation. A law that goes into effect on Jan. 1 allows computer users in the state to refuse unwanted solicitations en masse and sue spammers who violate their wishes for as much as ＄1 million. Those potent weapons for deflecting pitches that offer everything from bigger body parts to lower mortgage rates have attracted the ire of the U.S. Chamber of Commerce and mass marketers. Fearing the law will curtail advertising on the Internet, they are pushing for a far weaker national solution that would undercut the tough tactics in California and other states that are going the same route. But such self-interest is hardly enlightened. The growing flood of messages not only annoys PC users, it also slows the transmission of wanted e-mail and forces businesses to spend billions to combat spam. In fact, a survey released Oct. 22 suggests the proliferation of pitches could hurt the very e-commerce these business groups say they want to preserve. The survey of computer users, funded by the Pew Charitable Trusts, a non-profit group that studies public issues, found 25% use e-mail less because of spam. And 75% were reluctant to give out e-mail addresses, even to online retailers. The growing flood of messages not only annoys PC users, it also slows the transmission of wanted e-mail and forces businesses to spend billions to combat spam.