Specter has questioned the legality of the programs and proposed legislation that would bar President Bush and future administrations from bypassing 1970s-era laws requiring court approval for the surveillance of Americans. Specter has sought to hold hearings on the issue.
The White House has insisted that the president has the authority to authorize such operations because of his extensive wartime powers as commander in chief.
In his letter, Specter also said he had been told by other Republican members that "the telephone companies had been instructed not to provide any information to the committee as they were prohibited from disclosing classified information." Specter warned that his committee would "consider confronting the issue with subpoenas" if the White House persisted in seeking to block hearings on the matter.
Democrats quickly seized on the issue.
"The interference by the vice president in the Senate's efforts to conduct oversight of the White House's domestic spying program is deeply troubling," said Sen. Harry Reid (D-Nev.), the Senate minority leader.
"Just as disturbing is the fact that Senate Republicans have once again decided to deny the American people real oversight of the administration's actions."
*
Times wire services contributed to this report.
