n the toughest move to date against unsolicited commercial e-mail, Virginia enacted a law yesterday imposing harsh felony penalties for sending such messages to computer users through deceptive means.

The law would be enforced against those who use fraudulent practices to send bulk e-mail, commonly known as spam, to or from Virginia, a state that is headquarters for a number of major Internet providers, including the nation's largest, America Online.

The new statute adds criminal penalties for fraudulent, high-volume spammers. It outlaws practices like forging the return address line of an e-mail message or hacking a computer to send spam surreptitiously. Those found guilty of sending more than 10,000 such deceptive e-mail messages in one day would be subject to a prison term of one to five years and forfeiture of profits and assets connected with these activities.

Public outrage at spam is causing states and Congress to start looking at stronger measures against it. The Internet industry estimates that spam represents nearly half of all e-mail sent. And a new report by the Federal Trade Commission yesterday found that two-thirds of spam is sent with either false return addresses or a misleading subject line.

Such anger from computer users is even causing some in the industry to support federal legislation, if only to avoid having to deal with a patchwork of state anti-spam laws. More than two dozen states have anti-spam laws, but enforcement problems and low penalties have made many of the laws ineffective.

Virginia's governor, Mark R. Warner, said the new law could have a significant effect on spam because half of all Internet traffic flows through the state. The passage of e-mail through Virginia-based Internet service providers, he said, gives state prosecutors the ability to reach the purveyors of spam in other states and jurisdictions, noting that an earlier, weaker state anti-spam law had survived constitutional challenges.

"Many spammers see the current system that imposes civil fines as just a cost of doing business," Governor Warner said. "We hope we will see some high-profile prosecutions. If someone faces a jail sentence and a major forfeiture of assets, it will serve as a deterrent."

But some legal experts said they doubted whether Virginia would have as much of an impact as Mr. Warner suggested. Legal cases, they said, would probably be bogged down by questions over jurisdiction. Moreover, there are practical problems that limit the ability of prosecutors to reach beyond their own states.

Shane Ham, a senior analyst who studies anti-spam legislation for the Progressive Policy Institute, said, "I can't imagine the state attorney general in Virginia getting a lot of cooperation if they call up the police in California saying that they want them to arrest and extradite someone who is wanted for spamming."

About half the states have tried to regulate various aspects of spam. The first bill was passed in Nevada in 1997, and simply required that marketers offer recipients a way to be removed from e-mail lists. Washington state has brought several anti-spam cases based on laws that prohibit sending e-mail to state residents where the sender or the subject line is falsified.

Some states, including California, require unsolicited e-mail to be identified with "ADV" in the subject line. Some of these allow recipients of e-mail that violates these rules to sue the sender and seek monetary damages.

Experts say these state rules do not appear to have had a significant effect on spam but have instead perplexed big corporations, like credit card companies and catalog merchants, that do business by e-mail.

"We need a single strong national policy to deal with spam so that no one can play the states off against each other," Mr. Ham said. Of course, even national legislation would do little to prevent spam sent from overseas, as a great deal is.

Congress, which ignored anti-spam bills introduced in the last four years, is now expected to give serious consideration to several new proposals. Indeed, prospective Congressional action is, in part, a response to anti-spam efforts by the states.

The Direct Marketing Association, the lobbying group for companies that sell by postal mail and e-mail, has reversed its previous opposition to national anti-spam legislation, largely to secure a more unified set of rules.

The group would particularly like to avoid provisions that could force marketers who are found to violate the law to make payments to individuals who received their e-mail messages.

Earlier this month, Senators Conrad Burns, Republican of Montana, and Ron Wyden, Democrat of Oregon, introduced a bill that would require senders to label unsolicited commercial e-mail and ban them from falsifying the sender's name or the subject.

This week, Senator Charles E. Schumer of New York introduced a bill, intended, he said, to impose criminal penalties on senders who repeatedly violate the law and to create a national registry of people who do not want to receive spam. "Last year, spam was an annoyance," Mr. Schumer said yesterday. "This year, it is a significant problem, and next year, it could start to really kill the use of e-mail."

Representative Zoe Lofgren, Democrat of California, plans to introduce a bill that, like some state statutes, would require bulk spam to be labeled with "ADV" in the subject line. The bill would also carry out a proposal by Prof. Lawrence Lessig of Stanford forcing the senders of spam to pay computer users a bounty for reporting it.

All these proposals are meant to restrict deceptive marketers — those selling things like rich-quick schemes and penis enlargers — as well as merchants of pornography. They do not address the great quantities of nondeceptive marketing e-mail sent by big companies and even the Internet service providers themselves. America Online, for example, sends nearly two million marketing e-mail messages a day to its 35 million members.

But the diffuse nature of the Internet defies orderly regulation, even at the national level, when e-mail travels from state to state and country to country, often in untraceable ways. Many experts think that fighting spam will require new technological approaches that supplement legislation coming from many sources — including spam purveyors, Internet access providers and big companies that seek customers by e-mail.

Many anti-spam proposals will be debated in a three-day forum on spam in Washington starting today. The F.T.C. — which already prosecutes some spammers using existing anti-fraud laws — is organizing the forum and will take an unusually comprehensive look into the technology and economics of the spammers and the potential techniques to thwart them.

E-mail marketers, like Scott Richter, president of OptInRealBig.com, of Westminster, Colo., will debate with anti-spam activists like Alan Murphy, an investigator for Spamhaus, a British registry meant to identify spammers. (Mr. Richter is prominent on Mr. Murphy's list.)

Even Mr. Richter now says that a national law may be a good idea. "I want one law," he said in an interview. "Now, if someone lives in certain states, I have to put `ADV' in the header. What if he moves and I don't know it?"

Mr. Richter, however, does not want rules that would restrict his marketing too much, where he sells diet pills, among other things. "I'm a U.S. citizen and I've worked hard to build this business," he said. "I don't want to have to move to the Bahamas or to China."

Gov. Mark R. Warner of Virginia before signing a spam control law at the America Online headquarters outside Washington.

Charles Stiles, center, technical manager for America Online's antispam team, says a "a filter that works one day will likely not work the next."