The chairman of the U.S. Senate committee that will look into the Bush administration's domestic spying program next month promises to do a throrough investigation.

Republican Senator Arlen Specter said on U.S. television (ABC's `This Week') Sunday that the Senate Judiciary Committee will explore the program "in depth" when it holds hearings next month.

The Bush administration has said that a congressional resolution passed after the September 11, 2001 attacks to authorize use of military force also allowed without the usual court permission eavesdropping on international phone calls and e-mails from persons believed to be terror risks.

But Specter said Sunday that he doubts the congressional vote allowed domestic spying.

Specter said that in theory the president could face impeachment charges if found guilty of acting unconstitutionally. But he added there is no talk of that nd said no one doubts the president is making a good faith effort.

Some information for this report was provided by AFP, AP and Reuters.