In a dramatic escalation of his battle with the Secret Service, Whitewater prosecutor Kenneth Starr has subpoenaed the head of President Clinton's security detail to testify in the Monica Lewinsky investigation, two government officials said Tuesday.

Starr's move to compel testimony from Special Agent Larry Cockell was part of a sweeping new attempt to pierce the agency's cloak of confidentiality. At least four uniformed division officers also were subpoenaed, and Starr demanded Secret Service documents detailing Clinton's nighttime whereabouts between 1995 and 1997.