Sen. Ted Stevens

WASHINGTON — Sen. Ted Stevens accused the Justice Department of trampling on the independence of Congress, arguing Thursday that the corruption case against him should be thrown out.

That legal argument will test the limits of a court ruling that prosecutors fear could limit their ability to investigate corruption on Capitol Hill. Stevens said FBI agents went too far when they questioned his Senate aides.

The Alaska Republican is scheduled to go on trial next month on charges that he lied on Senate disclosure records about hundreds of thousands of dollars in gifts and services he received from a powerful oil services contractor, VECO Corp.

Stevens said the FBI's long-running corruption probe intruded on his Senate affairs. He cited the Constitution's speech-or-debate clause, which prohibits the executive branch from using its law enforcement authority to interfere with legislative business.

The Justice Department predicted this would happen after an appeals court ruled last year that the FBI violated the Constitution by searching the Capitol Hill office of Rep. William Jefferson, D-La. The Supreme Court refused to reconsider the case, and prosecutors said lawmakers already had begun arguing that their aides could not be questioned.

Legislative staffers have proven to be crucial witnesses in recent corruption cases. If Stevens prevails on this issue, it would be a blow to the Justice Department's power.

Anticipating Stevens' argument, the Justice Department filed its own court documents Thursday night, saying legislative speech issues were irrelevant.

"The government's criminal case against Senator Stevens is not based on his legislative activities but on his receipt of financial benefits and his need to conceal those benefits from public scrutiny," prosecutors wrote.

Prosecutors also officially acknowledged for the first time that they taped telephone conversations between Stevens and VECO founder Bill Allen.

In court documents Thursday, Stevens also argued that it's up to the Senate, not the Justice Department, to enforce Senate rules about financial disclosure. If the Senate feels he violated its rules, it can punish him, he said.

Stevens, the Senate's longest-serving Republican, has been a political force in Alaska since before it became a state. He has been dogged by the corruption case and now faces a challenge in the Republican primary.

He asked for an unusually speedy trial that he hopes will clear his name in time for the November election.

VECO employees normally build oil drilling and processing equipment. But VECO workers led the renovation of the senator's home, a project that was overseen by company founder and longtime Stevens friend Bill Allen. Stevens says he paid every bill he received.

Prosecutors say he got hundreds of thousands of dollars in freebies and discounted work that Stevens should have disclosed.

Though prosecutors say he also performed official Senate actions that benefited VECO, they don't accuse him of bribery.

In their filing Thursday, prosecutors outlined a series of conversations and e-mails in which Stevens apparently offered VECO help. In particular, prosecutors describe his help pushing for an Alaskan natural gas pipeline that would have benefited VECO. In one 2006 conversation, Stevens told Allen he would try to use his Washington connections to push forward the stalled pipeline deal.

The pipeline never materialized. Stevens' supporters have maintained that the senator long has supported the pipeline project, well before the VECO case.

Stevens also set up a meeting between VECO and the Federal Emergency Management Agency, prosecutors said.

Stevens' attorneys said Thursday that prosecutors were trying to insinuate bribery without actually charging it. They asked a judge not to let jurors see a paragraph in the indictment about those official actions.

"This language is blatantly inflammatory and prejudicial," attorneys wrote.