An investigation into possible ethics breaches by Republican vice-presidential pick Sarah Palin will be completed by October 10, three weeks earlier than scheduled, Alaska lawmakers said.

The probe would be ready earlier than expected in order to avoid the appearance of a politically-motivated "October surprise" ahead of the November 4 election, Alaska House judiciary chairman Jay Ramras said in a statement.

The statement added that Alaska Governor Palin would not face a subpoena ordering her to report for questioning, with lawmakers expressing confidence she would co-operate with investigators.

"We agreed that an earlier completion date was achievable, and that it was fair to all sides. We are satisfied that the report can be finished by no later than October 10, 2008," Ramras said.

Palin is being investigated by Alaska's legislature over allegations arising from the sacking of the state's public safety commissioner, Walt Monegan, who was fired earlier this year.

The probe was triggered after reports that Monegan was removed because he refused to fire a state trooper who was the governor's ex-brother-in-law, that the Palin family regarded as a "loose cannon."

The investigation -- dubbed "Troopergate" -- followed Monegan's dismissal in July. Palin has consistently denied that she put pressure on Monegan to fire the trooper involved, describing the allegations as "outrageous" and "false."

However it emerged on August 13 that there had been more than 20 calls, emails and other communications from Palin's office to employees at Monegan's Department of Public Safety.

Commenting on the decision not to subpoena Palin, on Friday, Alaska lawmaker Nancy Dahlstrom said investigators were satisfied she would co-operate.

"We also discussed and agreed amongst ourselves that no subpoena will be issued for the Governor," Dahlstrom said.

"She has told the public that she intends to cooperate with the investigation, indeed, she has told the public that she welcomes the investigation and I have every faith that she means it."