America Online Inc. has launched an intensified legal assault on junk e-mail by filing five lawsuits against more than a dozen individuals and companies accused of being major purveyors of "spam."

AOL, the nation's largest Internet service provider, with 27 million subscribers, said the targets of its suits were responsible for sending its members an estimated 1 billion pieces of spam that resulted in more than 8 million complaints. The unsolicited messages contained such things as pornographic images, body-enhancement offers, and diet and financial schemes.

The barrage of lawsuits reflects a heightened industry, legal and legislative effort to combat spam, which has grown so rapidly that it accounts for nearly 40 percent of e-mail traffic and is estimated to cost U.S. businesses $8 billion to $10 billion a year.

"Clearly, our anti-spam message is made more audible when the volume is turned up," said AOL spokesman Nicholas J. Graham. For the first time, Graham said, AOL is using member complaints about spammers as the basis for legal action.

The defendants in the lawsuits "are some of the leadership targets in the war against spam," he said. "They operate the command and control facilities in the ongoing fight to get spam into the inboxes of our members."

Most of the major Internet providers, including EarthLink Inc., Microsoft Corp., Yahoo Inc. and AOL, have sued or are suing spammers and their affiliates. But as individual and corporate computer users get increasingly irate at the rising tide of spam, many Internet providers say they are ramping up their legal efforts, even invoking federal anti-racketeering statutes.

The AOL suits, filed in federal court in Alexandria, seek a total of $10 million in damages and a halt to the spammers' e-mail activities under a number of state anti-spam and federal computer-fraud laws. Four of the suits were filed yesterday; one was filed late Friday. The suits single out two spammers by name, including one Maryland-based seller of quick-weight-loss products and anti-virus computer software, and an alleged affiliated spammer in Washington state. Other defendants are as yet unidentified because AOL isn't certain who they are; spammers often disguise their ownership of computers that generate spam.

Spammers, who send out hundreds of thousands of e-mail messages at almost no cost, rely on increasingly sophisticated tactics to find computer users. Even those Internet users who avoid advertising their e-mail addresses may not avoid spam, because some spammers use computer programs to randomly generate likely addresses.

Atlanta-based EarthLink also has been active on the legal front, with lawsuits pending against more than 100 spammers. In one case decided last year, the company won a $25 million judgment against a Tennessee-based spammer.

Microsoft, which has focused legal efforts on stopping spammers from using software to "harvest" e-mail addresses from Web sites, said it plans significantly increased legal action this year.

Efforts to get Congress to pass the first federal anti-spam legislation also have kicked into high gear.

Last week, Sens. Conrad Burns (R-Mont.) and Ron Wyden (D-Ore.) reintroduced anti-spam legislation that failed in the last congressional session amid opposition by the direct-marketing industry.

The bill, which has the support of the major Internet service providers, would impose criminal penalties if bulk e-mailers disguise their identities and do not provide valid means of unsubscribing from e-mail lists. Currently, when users click the "unsubscribe" link in hopes of removing themselves from e-mail lists, they often are merely confirming their e-mail address for spammers to use later or to sell to other bulk e-mailers.

Sen. Charles E. Schumer (D-N.Y.) is preparing similar legislation, but his bill also would create a national do-not-spam registry akin to a do-not-call telemarketers' list that the Federal Trade Commission recently set up to battle unsolicited telephone sales.

Schumer said the telemarketing registry has been a major success and his bill would make it equally easy for computer users to place themselves on a list that would bar bulk e-mailers from sending them unsolicited commercial e-mail.

House bills are also expected.

The Direct Marketing Association, which lobbies for many companies that send commercial e-mail, wants fraudulent spammers stopped. But the industry worries about any legislation that would infringe on the ability of legitimate marketers to get their messages out.

So far, the association has praised Burns and Wyden for starting the debate on the issue and has said it will support some form of anti-spam legislation. But the group stopped short of endorsing the Burns-Wyden bill.

On the flip side, many technologists in the anti-spam community argue that only a ban on all unsolicited commercial e-mail will make a dent in the problem.

Most online marketers, and some of the Internet providers themselves, currently operate with an "opt-out" system in which users must actively choose not to receive commercial e-mail. So far, these firms have opposed moving to an "opt-in" system, whereby unsolicited mail would not be sent unless users specifically asked for it.

In the suits filed yesterday, AOL alleges that George A. Moore Jr., head of Maryland Internet Marketing Inc. in Linthicum, sent spam for cut-rate mortgages and packages of anti-virus software through another alleged spammer named in the suits, Michael Levesque of Washington state.

The suit alleges that Levesque also sent an extensive amount of porn-related spam. He could not be reached for comment.

Moore, who also sells health and weight-loss products such as Fat-N-Emy and Extreme Colon Cleanser, said he had not yet seen the lawsuit.

But he said that recent harassment by anti-spam vigilantes, including several death threats, is causing him to get out of the online sales business.

Moore gained notoriety when his home address and other information were posted on the Internet by an Ellicott City man who urged people to sue known spammers.

Moore then went to court to get the site pulled down because of the harassment that resulted, but last week a Maryland district court judge refused.

"It's just not worth it anymore," Moore said.