WASHINGTON -- Aides said Thursday that former House Speaker Dennis Hastert plans to resign from Congress sooner than expected.

The Illinois Republican announced in August that he would not seek re-election next year, but he had said he would finish his current term, which ends in 15 months.

Republican aides said he now intends to leave later this year or early next. That would trigger a special election in his Chicago-area district.

Republicans are hoping to hold the seat ahead of next year's general election, which some are fearing will draw large numbers of Democratic voters unhappy with President George W. Bush and the Iraq war.

Hastert has served 21 years in Congress and was the longest-serving Republican speaker in history. He held the post from January 1999 until Democrats took control of the House early this year.

Last year, Hastert came under fire in the midst of a scandal over inappropriate e-mails to House pages from former Florida GOP Rep. Mark Foley.

Foley was forced to resign in the scandal, and critics said that Hastert's office knew about the e-mails a year before they were made public, but did not intervene.

Hastert denied any wrongdoing in how his office handled the matter, and fought against efforts to force him from the speakership.