The Secret Service is investigating the publication of personal information about GOP convention delegates on a Web site, prompting complaints from the American Civil Liberties Union that the government is infringing upon the free-speech rights of political dissidents.

Federal authorities have subpoenaed Calyx Internet Access seeking to learn the Internet address of the person who posted a spreadsheet on Aug. 18 containing the names of about 1,600 delegates, along with their home addresses, phone numbers and e-mail addresses and the hotels at which they are staying in New York City.

The probe is directed at possible criminal violations of the law that prohibits voter intimidation, according to a subpoena to the Internet service provider dated Aug. 19. ACLU officials said Calyx has provided the government with names of four administrative contacts who run, the Web site that published the delegate information.

Matt Toups, a systems administrator for the site, said the Secret Service and the U.S. attorney's office, which requested the grand jury subpoena, are trying "to put heat on people who are involved in dissent." He said the activists who write in to his Web site and who have thronged protest marches in New York "should know more about who the delegates are so they can engage in picketing or letter writing."

Neither the U.S. attorney's office in New York nor the Secret Service would comment on the investigation.

The Aug. 18 posting said that "as a small contribution to the anti-RNC efforts, today we are releasing a list of delegates to the 2004 Republican National Convention. Our objectives are to: Supply anti-RNC groups with data on the delegates to use in whatever way they see fit."

Numerous postings on the site yesterday lauded protesters' efforts to target delegates. "Wherever they went, across the breadth of Manhattan island, RNC delegates were taunted, mocked, and generally harassed by activists and ordinary New Yorkers alike," one posting on the site said.

The ACLU publicized the subpoena on its Web site yesterday under the headline "Secret Service Investigation Aims To Chill Speech and Intimidate Protesters." Attorney Ann Beeson said that while the Web list was posted anonymously, it was derived from information that is publicly available.

Beeson said she knows of no security threat created by publication of the information about delegates. "Taunting them and mocking them is a time-honored form of political protest," she said.

The Aug. 18 Web article said the list information was gathered "from a variety of sources." It encouraged readers to e-mail additions to the list, promising that "contributed info will remain anonymous of course," and added that "we encourage the use of encryption."

Barbara Deuschle, left, of Hot Springs, Ark., and Mary Anne Kusaka of Hawaii make "W" gestures during the evening session of the first day of the Republican National Convention.A delegate finds a peaceful spot to rest above the bustling floor of Madison Square Garden.South Dakota state Rep. Gordon R. Pederson dresses the part for the convention.