He denied Democratic accusations that the removal of the lawyers was a purge by intimidation and a warning to remaining prosecutors to fall in line in supporting the Bush administration's agenda.
He also denied that the prosecutors were dismissed because of interference with corruption investigations.
Sampson said before the senate judiciary committee: "To my knowledge, nothing of the sort occurred here."
Sampson said the statement of Alberto Gonzales, the attorney general, which said that he was not involved in discussions about the fsacking of the eight US prosecutors, was false.
"I don't think the attorney general's statement that he was not involved in any discussions of US attorney removals was accurate," he said.
"I remember discussing with him this process of asking certain US attorneys to resign."
Sampson pointed out that prosecutors serve at the president's will and that it is legitimate to judge them on whether they pursue or resist administration policy.
"The distinction between 'political' and 'performance-related' reasons for removing a US attorney is, in my view, largely artificial," he said.
"A US attorney who is unsuccessful from a political perspective ... is unsuccessful."
The justice department admitted on Wednesday that it gave senators inaccurate information about the firings and role of Karl Rove, the presidential political adviser, in trying to secure a US attorney's post in the state of Arkansas for one of his former aides, Tim Griffin.
Justice officials acknowledged that a February 23 letter to four Democratic senators made an error in asserting that the department was not aware of any role that Rove played in the decision to appoint Griffin.
Richard Hertling, acting assistant attorney general, said that certain statements in last month's letter to Democratic politicians appeared to be "contradicted by department documents included in our production".
Sampson acknowledged planning the firings as much as two years ago with the judgement of a number of senior justice department officials.