WASHINGTON (AP) _ The head of President Clinton's Secret Service security detail arrived at the federal courthouse today under subpoena requiring his testimony in the Monica Lewinsky investigation.

Special Agent Larry L. Cockell entered the courthouse after the Clinton administration unsuccessfully attempted to gain him a last-minute reprieve from testifying. But Justice Department lawyers were expected to carry the challenge to a higher court.

Cockell was surrounded by law enforcement officers as he entered an elevator for the grand jury floor of the courthouse.