WASHINGTON – Campaign finance laws could lead to the suppression of pointedly partisan books unless regulators expand their definition of “the press,” according to the chairman of the Federal Election Commission, Bradley K. Smith.

Election-year books such as “Bush Must Go: The Top Ten Reasons Why George Bush Doesn’t Deserve a Second Term,” by Bill Press, and “Unfit for Command: Swift Boat Veterans Speak Out Against John Kerry,” by John E. O’Neill and Jerome R. Corsi, contain the kind of “express advocacy” against specific candidates that cannot be paid for by corporate funds.

“These could be subject to government regulation (and potentially suppression) under the campaign finance laws, because they appear to expressly advocate the defeat of a clearly identified federal candidate, and are produced and promoted by corporations,” wrote Mr. Smith in a little-noticed concurrence to a commission advisory opinion last week.

Federal campaign finance law prohibits any corporation from making a “contribution or expenditure in connection with any federal election.” Forbidden expenditures include money spent “for the purpose of influencing any election for federal office.”

While newspapers, magazines, and broadcasting stations are excluded from this restriction, the so-called press exemption has been interpreted narrowly by the courts and the commission, Mr. Smith noted.

The question of who qualifies as the press is becoming one of the most pressing and vague issues facing the commission as new groups and technologies push the boundaries of traditional journalism, legal experts said yesterday. The National Rifle Association has purchased a satellite radio channel to disseminate its views, and Michael Moore’s anti-Bush polemic, “Fahrenheit 9/11,” has been a mainstream commercial success.

“Politics is now entering new media outlets in a fashion that we have not experienced before,” said a campaign finance lawyer, Jan Baran, whose clients have included the Republican National Committee and large entertainment corporations.

“Neither the constitutional nor legal structure has really grappled with those issues in any refined way. They are bouncing around trying to figure out what is the freedom of press,” Mr. Baran said.

On Friday, the commission ruled unanimously that a conservative advocacy group called Citizens United was not entitled to a press exemption to promote a documentary or book entitled “The Many Faces of John Kerry, Why This Massachusetts Liberal Is Wrong for America.”

The group did not have a “commercial interest” in promoting the book, and it had planned to pay to air the film, rather than to make money off it. It also did not have a history of book publishing, and its activities would not be part of a “normal, legitimate [media] function,” the commission found.

Campaign finance specialists yesterday agreed that the press exception remains imprecise, though most predicted that established publishers would be protected.

A professor of law at Ohio State University who specializes in election law, Edward Foley, said the chairman raised a legitimate point.

“Books that contain express advocacy would appear to be subject to federal campaign finance rules and not eligible for the media exception, unless an argument could be made that mainstream publishers who spent money to produce and distribute those books do so without a campaign motivation,” he said.

“This is a new issue and there is some confusion as to how far the media exception will go,” said a campaign finance lobbyist at Public Citizen, Craig Holman. He said the commission should hold hearings and specify its rules defining the press. Mr. Holman predicted publishers would be protected as long as they were engaged in a “business enterprise” and accused the chairman of “playing chicken little” with his warning.

As long as the publisher is publishing a book to make money and not to help a candidate, it is exempt from the law, said the founder of the Campaign Finance Reform Working Group at the American Enterprise Institute, Norman Ornstein.

“If a regulatory body is doing its job with attention to the intention of the law and the letter of law, you will find that there are few cases that are ambiguous,” he said.

Mr. Baran agreed that the commission would be unlikely to prohibit books published by established publishers, but he said the definition could have an impact on “vanity presses” and independent start-up operations.

“I think if election laws were consistent and applied in a consistent fashion, [Mr. Smith’s] point would be valid. I think his point is a lot of these distinctions are nonsensical and illogical,” he said.