A federal grand jury investigating leaks of classified information has summoned a former National Security Agency officer who says he talked to reporters about the agency's warrantless eavesdropping program.

Russell Tice received a subpoena to testify next Wednesday to a grand jury that is meeting in Alexandria, Va. The subpoena was posted Friday on a Web site run by a whistleblowers' group to which Tice belongs.

"The grand jury is conducting an investigation of possible violations of federal criminal laws involving the unauthorized disclosure of classified information," according to a letter that accompanied the subpoena.

In response to the subpoena, Tice said, "This latest action by the government is designed only for one purpose: to ensure that people who witness criminal action being committed by the government are intimidated into remaining silent."

Tice has said he spoke to reporters for The New York Times prior to the newspaper's story in December that disclosed the NSA program that intercepts Americans' international telephone calls and e-mails without a court's approval.

President Bush later confirmed the program's existence. Calling the program an important anti-terror tool, Bush has defended it against criticism that it illegally sidesteps a secret court set up to decide whether surveillance warrants should be issued in terrorism and espionage cases.

The Justice Department launched a leaks investigation in December.

Tice has said the NSA fired him last year after he suggested there could be Chinese spies in the U.S. intelligence community. He said his dismissal was retaliation for his raising the issue of espionage.

When the NSA program was disclosed in December, Tice said publicly that he had information about "probable unlawful and unconstitutional acts" involving the NSA director, the defense secretary and other officials as part of highly classified government operations.

Tice has offered to testify to Congress about what he knows.

Tice's statement was posted on the National Security Whistleblowers Coalition Web site: http://www.nswbc.org.