Millions of Americans who are already trying to fight off unwanted electronic mail from direct marketers are about to get deluged by another source: politicians and lobbying groups.

For the first time, a nationwide list of registered voters has been cross-referenced with multiple lists of e-mail addresses collected from magazine subscribers, catalogue shoppers, online poll participants and the like. The result is that legislators, candidates for office and interest groups can buy more than 25 million e-mail addresses of registered voters and contact them at will.

"This is the next generation of campaign strategies," said Roger Alan Stone, chief executive of Advocacy Inc., the D.C. cyber-consultancy that helped create the new product. (He is not the well-known Republican consultant of the same name).

But privacy advocates are appalled by the development. They see Stone's enterprise as dangerously intrusive and potentially harmful to the public's confidence in government. "What we're talking about here is political spam," said Pam Fielding, co-author of "The Net Effect: How Cyberadvocacy is Changing the Political Landscape."

Direct-mail marketers have long used voter registrations to locate street addresses and then send what's often called junk mail. But the pairing of voter registrations with e-mail addresses is new and involves the use of what's widely considered to be private information. Personal e-mail addresses are not as available as street addresses are, and they are acquired for this use without the owner's explicit consent.

In addition, e-mails can be sent in such large numbers and at so little cost that voters can be repeatedly targeted. The mailings can be tailored to voters' personal, even intimate, information. Advocacy Inc., for instance, can easily sort its e-mail lists by political party, voting frequency, age, gender, ethnicity and geography right down to neighborhood.

"Many constituents are likely to be incensed at such minute targeting; to them it will feel a lot like Big Brother is watching," Fielding said.

"We've been moving toward this for a long time," said Ari Schwartz, associate director of the Center for Democracy and Technology, an Internet watchdog group. "But most Americans still don't realize how frequently their information is sold to the highest bidder and that politicians are now operating in that same marketplace."

Other leaders in electronic lobbying have decided against putting together a similar list for fear of sparking voter outrage. For example, Aristotle International Inc., which maintains a 50-state voter registration file, "has repeatedly declined arrangements that would even appear to compromise privacy or utilize deceptive e-mail marketing," said Dean Aristotle Phillips, the company's president. "Given the pervasiveness of spam, responsible campaigns, organizations and vendors reject the deceptive methods of spammers."

Until now, reputable owners of e-mail databases have refused to sell their addresses unless the buyer could demonstrate a direct connection to potential future recipients. For instance, lobbying groups could legitimately get the e-mail addresses of their members or donors. But Advocacy Inc. has argued that all registered voters have a clear interest in the democratic process and therefore are natural recipients of e-mails from any political organization.

Stone denies he's spamming anyone. Filters do not consider his company's e-mail to be spam because of the kind of servers that send it. He said e-mail recipients can click a link if they don't want to receive political communications. He also said that since he launched the lists this year, the complaint rate has been low. In addition, the service is so useful to his customers that he expects huge sales for the list. "Now any candidate or interest group can call us up and ask, 'How many Democratic voters do you have e-mails for in Ohio?' or 'How many non-registered voters do you have e-mails for in Florida between the ages of 18 and 24?' and we can get it to them in a couple hours," Stone said.

Business has been brisk. Stone said he has 60 clients, including 20 members of the U.S. House of Representatives, 15 candidates for Congress, nine state or local ballot initiatives and a dozen interest groups including the Union of Concerned Scientists and the Council for a Livable World. "We are adding at least 10 new clients a week and the pace is growing rapidly," he said.

"It could go like gangbusters" until Election Day, said William Daly, chairman of Voter Contact Services (VCS), the owner of the national, 155 million-person voter file that Stone's company matched with e-mail addresses. Daly reports that the e-mail list has been selling especially well in Ohio, New York, California and Hawaii.

MailFrontier Inc., an e-mail security and anti-spam company, estimates that more than 1.25 billion unsolicited political e-mails will be sent to registered voters this year, up from virtually none during the last presidential election. One reason is that commercially available e-mail databases are larger and can be tapped to produce substantially sized lists. E-mailing has also become more routine. In addition, said Deanne Phillips, a spokeswoman for MailFrontier, "It costs a lot less to send e-mails versus postal mail or TV advertising."

In New York City, Democrat Frank Barbaro is trying to unseat Rep. Vito Fossella (R) with the help of 70,000 e-mail addresses acquired from Advocacy Inc. Barbaro aides said the former state Supreme Court justice plans to contact all of these registered voters once or twice a week until the election with carefully tailored messages. For instance, Democratic women in one part of Brooklyn will receive e-mail about Barbaro's opposition to real estate development there. Men registered as independents will get a more generic point of view.

And all of it will cost very little. A single, paper mailing to 70,000 voters would run about $35,000, said Barbaro spokeswoman Denise Devlin. In contrast, the campaign bought the 70,000 e-mail addresses from Advocacy Inc. for 15 cents each (or about $10,500), pays the company $1,000 a month to maintain them and can use them for free whenever it wants. "We can communicate with voters quickly and inexpensively," Devlin said.

Another Advocacy Inc. customer -- a pro-tax-cut group in Pennsylvania called Philadelphia Forward -- sent 2 million e-mails to voters over two weeks this year and instigated 80,000 anti-tax faxes to City Hall. In Arizona, the Democratic Party is using e-mail lists purchased from the company to persuade voters to sign up for absentee ballots and vote early. "The coupling of e-mail with vote-by-mail is a very powerful combination," said Bob Grossfeld, a Phoenix political consultant.

One of the largest clusters of users of off-the-shelf e-mail lists are members of Congress. Last fall, the House of Representatives voted to give e-mail a privileged place in its franking system -- the system under which lawmakers use taxpayer money to pay for communications with their constituents. Since then, dozens of legislators have been paying companies like Stone's to organize their e-mail programs and get their constituents' e-mail addresses. According to the House Administration Committee, at least 130 lawmakers in the 435-member House send e-newsletters to their constituents.

In February, Rep. Nancy Pelosi (Calif.), the Democrats' minority leader in the House, invited three electronic lobbying firms to a private meeting of the entire Democratic Caucus at West Virginia's Coolfont Resort. The three firms, which lectured the members of Congress on cutting-edge e-mail methods, were Stone's Advocacy Inc., Democratic Network, and DCS Congressional, a firm part-owned by former Rep. Tom Downey (D-N.Y.) that's affiliated with an electronic lobbying venture.

Republican lawmakers are also hiring e-mail consultants. The GOP e-lobbying firms that have branched out into lawmakers' offices include Rightclick Strategies, Constituents Direct and Integrated Web Strategy. Integrated Web Strategy of Phoenix is run by Max Fose, the 32-year-old computer whiz who four years ago helped popularize the use of the Web for political fundraising, which is now burgeoning. At the time, he was Internet manager for the presidential campaign of Sen. John McCain (R-Ariz.).

Lawmakers pay lobbying firms like these between $6,000 and $20,000 a year to compile their constituents' e-mail addresses, keep track of their correspondence and often recommend how to compose e-newsletters. Legislators who use the service say that's a small price to pay given its speed and efficiency. "It doesn't cost us much and there's no folding or stuffing," said Jack Pratt, chief of staff to Rep. Steve Israel (D- N.Y.). "You push a button and it's gone."

Lawmakers get an extra benefit, too. They can communicate electronically with anyone who subscribes to their newsletters right up until Election Day, something that's forbidden for the old, snail-mail-style of franked correspondence. The ability to contact 10,000 or more constituents right before an election gives an incumbent a significant advantage.

"Normally they [members of Congress] are asking me for money," Downey said. "This is a sort of turnabout-is-fair-play situation."

Some critics say the arrangement is too fair. "There's certainly the danger of a conflict of interest here," said Schwartz of the Center for Democracy and Technology. "The same firm that's creating a [House] member's e-mail box also wants to flood that same box with e-mails from outside groups. Lawmakers have to be wary."

Ryan Turner, policy director of the nonprofit Community Technology Centers' Network, thinks the threat goes beyond appearances. He worries that the lists firms compile could be abused unless safeguards are in place to prevent them from selling to their lobbying clients the e-mail addresses they collect for lawmakers.

For their part, the lobbying firms scoff at such fears. They say they function as arm's-length consultants and keep their hands off the lawmakers' e-mail lists. "We're only providing technical services," Stone said. "The lawmakers have full ownership of the list and we don't."

Nor do Stone and VCS's Daly worry about critics who complain that their national e-mail list is merely an invitation to spam. "Nobody really wants to get political advertisements, but elections do get run and people communicate," Daly said. "How people react to this e-mail, assuming they get a whole lot of it, is going to be very interesting to see."

Advocacy Inc. chief executive Roger Alan Stone, left, and senior vice president Rob Stuart helped create the list, which cross-references voter registration with e-mail addresses. Stone has 60 clients, including House members.